Transcription is the first step, where a segment of DNA is copied into RNA, and translation follows, where the RNA is used to build proteins. Together, these processes ensure the flow of genetic information within cells, ultimately supporting growth, repair, and various biological functions. Understanding these steps is key to unraveling the complexity of life at the molecular level.

The structure of DNA

DNA is a double-helix structure consisting of two antiparallel strands, with a sugar-phosphate backbone forming the outer framework and nitrogenous bases creating the inner steps of the twisted ladder. The four nitrogenous bases—adenine (A), thymine (T), cytosine (C), and guanine (G)—pair specifically: adenine with thymine and cytosine with guanine, held together by hydrogen bonds.

This sequence of bases encodes genetic information, determining traits and cellular functions. The structure of DNA allows for accurate replication, ensuring the transfer of genetic material to future generations. Additionally, the outer edges of the bases are available for interactions with other molecules, enabling essential biological processes like replication and transcription.

On a structural basis, there are three types of DNA: A-DNA, B-DNA, and Z-DNA. Out of these three, B-DNA is the most common DNA in normal conditions. It consists of minor and major grooves with a diameter of 20Å and a length of 34Å. It consists of 10.5 base pairs in one turn with a pitch of 3.4Å. The stable structure provides an essential template for transcription, where one DNA strand acts as a template for RNA synthesis, forming complementary base pairs through phosphodiester bonds. The opposite strand, known as the coding strand, carries the same sequence as the transcribed RNA (thymine is replaced with uracil in RNA.

The role of DNA structure in storing genetic information

The double-helix structure of DNA has evolved for storing and transmitting genetic information, unlike RNA. DNA encodes information both digitally (through specific base sequences for amino acids) and analogously (through physical properties like stiffness and strand separation).

Key advantages of the double-helix structure include:

• Stability – The helical shape shields nitrogenous bases by positioning them internally.
• Efficient packaging – DNA can be compactly organized into chromosomes.
• Accessibility – The structure allows easy access to genetic information when needed.

The DNA has a twisted and helical shape, which also enables supercoiling and plays a role in gene regulation, chromosome organization, and providing energy for enzymes like RNA polymerase.

The stability of the DNA double helix relies on the following:

• Specific base pairing (A with T, G with C) through hydrogen bonds creates a reliable coding system, ensuring precise replication and genetic information storage.
• The backbone of DNA is composed of alternating sugar and phosphate molecules that create a negatively charged exterior, shield the genetic bases, and offer structural stability. The DNA helical structure has both major and minor grooves. The major groove provides proteins with access to genetic material, while the minor groove provides additional binding sites to regulatory proteins, enabling intricate control of gene expression.

The overall DNA structure is water-soluble, with the hydrophobic bases shielded from the surrounding environment. Additionally, DNA can be tightly compressed through various structural configurations, with histones—proteins around which it coils—playing a key role in this process. By effectively coiling around histones into chromatin, the DNA molecule can further condense into chromosomes, making it possible to store a vast amount of information in the little area of a cell nucleus. DNA can last hundreds of years under the right conditions, making it one of nature’s most impressive information storage systems¹.

DNA transcription

Transcription is the process by which the DNA sequence of a gene is converted into RNA. During this process, different types of RNA are produced, including messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA), all of which are crucial for protein synthesis. Each RNA type—mRNA, rRNA, and tRNA—follows its own synthesis pathway and plays a vital role in protein production and other cellular functions.

Transcription occurs in both prokaryotes and eukaryotes, although the mechanisms differ between these two groups. In prokaryotes, transcription occurs in the cytoplasm, while in eukaryotes, it takes place in the nucleus before the RNA is processed and transported to the cytoplasm for translation. The field of RNA biology is complex, with discoveries adding novel roles for other RNA molecules, such as non-coding RNA molecules.

Significance in gene expression

Gene expression is the process through which information from a gene is used to create a functional product, typically a protein. These proteins serve as enzymes, hormones, primary antibodies, and structural components, enabling the body to carry out essential processes like metabolism, growth, immune defense, and tissue repair.

Gene expression ensures that the right proteins and peptides are produced at the right time and in the right amount, which maintains proper cellular function and health of the organism. Any disruptions in gene expression can lead to various diseases, including cancer, genetic disorders, and autoimmune conditions.

DNA arrangement (chromatin), transcription factors, and modifications exhibit dynamic and intricate interplay when expressing a gene. An example is DNA methylation, the regulation that prevents transcription factors from binding to DNA and subsequent transcription. Further, changes in DNA methylation (and hence, transcription) are seen in aging and its associated disorders.

Role of RNA polymerase in the transcription process

In the transcription process, RNA polymerase (RNAP)is responsible for synthesizing RNA from a DNA template.

In prokaryotic cells, a single RNA polymerase complex, consisting of four core subunits and a sigma subunit, initiates transcription by binding to the DNA at the gene promoter region and synthesizing RNA in the 5’ to 3’ direction. The E. coli RNA polymerase has 5 sub-units: α (two copies), β, β′, and ω subunits, and much research (around fifty years of work) is available on this molecule. The β and β′ subunits account for 80% of the total mass of the core enzyme, and are mostly conserved over evolution.

In eukaryotes, however, distinct RNA polymerases are involved in the synthesis of different types of RNA, with RNA polymerase I producing rRNA, RNA polymerase II synthesizing mRNA, and RNA polymerase III responsible for tRNA synthesis.

Steps in DNA transcription

DNA transcription steps include promoter recognition, initiation, elongation, and termination, which are conserved across species but vary in complexity levels and mechanisms.

Initiation

Initiation of transcription begins with the assembly of RNAP and transcription factors (TFs) at the promoter, leading to several conformational changes that form the initiation complex. The search for the promoter by RNAP entails specific kinetics. Furthermore, the promoters are considered central regulatory features.  The initiation process involves:

• RNAP binds to the DNA template, creating a pre-initiation complex.
• DNA is bent to form the RNAP-promoter closed complex (RPc).
• RNAP then transitions to the RNAP-promoter open complex (RPo), unwinding the DNA and positioning it for RNA synthesis.

The transition from RPc to RPo is rate-limiting and influenced by factors like the sigma factor. RNAP synthesizes a short transcript during abortive initiation, a process governed by a “scrunching mechanism,” before either re-engaging in transcription or transitioning into the elongation phase.

The transcription initiation in eukaryotes is more complex than prokaryotes and involves multiple TFs that help recruit RNA polymerase II to the promoter. In this regard, TFs are called “master regulators,” with an estimated 1,600 presumed TFs encoded in the human genome.

Elongation

During the elongation phase, RNAP moves downstream from the promoter, forming a “transcription bubble” called the elongation complex (EC), where it synthesizes RNA in the 5′ to 3′ direction by the addition of the required ribonucleotide.

RNA polymerase in prokaryotes synthesizes RNA efficiently with the help of conserved elongation factors like NusG, NusA, GreA, and Mfd, and its activity is regulated by the concentration of nucleoside triphosphates (NTPs).

In eukaryotes, RNA polymerase II transcribes protein-coding genes within a chromatin structure, requiring chromatin remodeling complexes to overcome nucleosome barriers. Chromatin is a compact structure of DNA, RNA, and proteins that form the backbone of chromosomes. DNA wraps around histone proteins to form nucleosomes that condense into chromatin fibers. This structure facilitates extensive packaging of DNA within the nucleus while also controlling essential processes such as replication, transcription, repair, recombination, and cell division. Additionally, eukaryotic elongation is regulated by phosphorylation of RNA polymerase II’s C-terminal domain (CTD), which recruits elongation factors to ensure efficient transcription.

An interesting observation here is the ability of RNA polymerase to backtrack along the template and pause at certain sites (this is subject to much research, given that it can decide the fate of the transcript).

Termination

Transcription termination entails three mechanisms: intrinsic hairpin formation, and Rho-dependent and Rho-independent pathways. The Rho factor is an essential termination factor that pulls mRNA from the elongation complex (EC). The role of Mfd (described as a transcription repair coupling factor) in dissociating the transcription complex is also documented.

Termination in eukaryotes involves additional steps like RNA polyadenylation and dephosphorylation of the CTD of RNA polymerase II and transcription factors, leading to detachment from transcription factors.

Processing of pre-mRNA in eukaryotic cells

The mRNA produced in eukaryotes during transcription is called precursor mRNA (pre-mRNA). The pre-mRNA undergoes extensive modifications to remain safe from degradation.

mRNA processing involves 5’ capping, splicing, 3’-end processing, and export. These modifications and associated protein factors regulate mRNA structure, expression, localization, and stability throughout its lifecycle.

Capping

5′end-capping of mRNA is the addition of a 7-methylguanosine cap at the 5’-end. This cap is evolutionarily conserved and plays a role in RNA maturation, export, and also innate immunity. The process  involves three enzymatic activities:

• RNA triphosphatase
• Guanylyltransferase
• 7-methyltransferase

This process begins shortly after RNA Pol II transcribes the first 25-30 nucleotides, with the RNA triphosphatase removing the γ-phosphate, followed by GMP transfer and subsequent methylation of the guanine.

Polyadenylation

Polyadenylation involves endonucleolytic cleavage of the pre-mRNA downstream of a conserved signal sequence (AAUAA in mammals) at the 3′ end of the mRNA. This reaction is followed by the addition of a poly(A) tail, which is important for mRNA stability and translation.

This process requires multiple proteins like cleavage and polyadenylation specificity factor (CPSF), Cleavage stimulatory factor (CstF), and poly(A) polymerase (PAP), and can include alternative polyadenylation, which influences mRNA stability, localization, and translation. There are at least a dozen associated factors that regulate this process, with abnormalities in the 3′ processing leading to several diseases, including neurological diseases and cancer.

Splicing

Splicing is the process by which non-coding introns are removed from messenger RNA precursors (pre-mRNA), and exons (protein-coding segments) are spliced together to form mature messenger RNAs (mRNAs). This reaction is catalyzed by the spliceosome, which includes small nuclear RNPs (snRNPs) like U1, U2, U4, U5, U6, and various proteins, such as small nuclear ribonucleoprotein (snRNPs), non-snRNP–associated proteins and protein complexes.

This process involves two transesterification reactions to join exons and release the intron:

• The branch point, 2′-OH, attacks the first nucleotide of the intron, forming a lariat intermediate.
• The 3′-OH of the free exon attacks the last nucleotide of the intron, joining the exons and releasing the intronic lariat.

Splice site selection is influenced by both sequence elements and regulatory factors, resulting in alternative splicing that contributes to gene expression diversity.

mRNA translation: Turning RNA into proteins

Protein translation is the process of synthesizing a specific sequence of amino acids to form a functional protein from the nucleotide sequence of mRNA. This process is fundamental for all living organisms, including viruses, to produce proteins vital for structure and function. The role of the genetic code becomes vital here, where a set of three nucleotides (called a codon) on the mRNA are read as an amino acid by the translation machinery; essentially, the language of the RNA (A, U, G, and C) becomes the language of the amino acids following the rules of the genetic code.

Translation involves initiation (ribosome assembly and recognition of the start: a start codon), elongation (amino acid addition by tRNA according to the mRNA codon sequence), and termination (release of the completed polypeptide upon recognizing a stop codon).

However, the deregulation of translation is increasingly recognized as a key factor in the pathogenesis of diseases like cancer, neurodegenerative, and cardiovascular conditions.

Components involved in translation

Translation is a complex process that occurs in both prokaryotes and eukaryotes. It consists of three major components:

• mRNA: mRNA is a linear molecule composed of nucleotides that contain codons, which are sequences of three bases encoding specific amino acids. Its function is to carry genetic information from DNA to ribosomes, where it serves as a template for protein synthesis.

• tRNA: The secondary structure of tRNA has a cloverleaf shape with two functional ends:

  • One end (the 3′ end called the CCA)  binds to a specific amino acid.
  • The other end contains an anticodon that pairs with the complementary codon on mRNA.
    Its function is to transport amino acids to the ribosome and ensure they are added in the correct sequence during protein synthesis. This is referred to as its function as an “adaptor” as it has the anticodon matching the codon sequence in the mRNA for the amino acid that is coded.

• Ribosomes: Ribosomes are universal structures made of complexes of ribosomal RNA (rRNA) and proteins. They have two subunits:

  • Large subunit – 70S (S is Svedburg unit referring to the sedimentation rate) in prokaryotes and 80S in eukaryotes
  • Small subunit– 30S in prokaryotes and 40S in eukaryotes
    Ribosomes are the site of protein synthesis, and they facilitate the assembly of amino acids into a polypeptide chain as directed by the mRNA sequence.

Steps of translation

The translation process involves initiation, elongation and termination. The result of these steps produces “nascent proteins.” The correct folding of the proteins and many post-translational modifications make the proteins functional.

Initiation

Aminoacyl-tRNA synthetases are the enzymes that charge tRNA molecules with their corresponding (cognate) amino acids. Translation begins when a ribosome assembles at specific signals called the “start codon” (usually AUG that codes for methionine) of mRNA, guided by initiation factors that ensure accurate initiation.

In prokaryotes, the 30S subunit recognizes the Shine-Dalgarno sequence on the mRNA, positioning the start codon, while initiation factors like IF1, IF2, and IF3 help recruit the initiator tRNA carrying the initiator tRNA-that is N-formylmethionine  (fMet) or methionine with a formyl group.

Translation begins with the cap-dependent recognition of the 5’ cap of the mRNA by the eIF4 complex, in eukaryotes. The 40S ribosomal subunit binds to this complex initiating the scanning process to locate the start codon (AUG). This is followed by the recruitment of the 43S pre-initiation complex and the assembly of the 80S ribosome, marking the transition to the elongation phase.

Elongation

Elongation is the process where the ribosome synthesizes the polypeptide chain by adding amino acids one at a time to the growing chain by allowing the entry of tRNAs carrying their amino acids, allowing bond formation, and allowing the exit of the empty tRNA molecules.

In both prokaryotes and eukaryotes, elongation requires the following three key factors:

• Elongation factors like EF-Tu in prokaryotes and eEF1 in eukaryotes attach tRNA to the ribosome,
• The ribosome itself that facilitates peptide bond formation
• Guanosine triphosphate (GTP) that supplies energy.

The larger unit of the ribosome consists of three key sites:

• The aminoacyl or A site, where tRNA enters with the new/next amino acid.
• The peptidyl or P site, where the growing polypeptide chain is held
• The exit or E site, where the tRNA exits after the amino acid attached to it, is added to the growing polypeptide chain.

The tRNA, bearing the correct amino acid, enters the A site, pairs its anticodon with the mRNA codon, and transfers the amino acid to the polypeptide chain in the P site. A peptide bond is formed between the amino acid of the A site and the P site. Peptidyl transferase catalyzes peptide bond formation in the large ribosomal subunit.

The ribosome then moves along the mRNA to the next codon in a process called translocation, facilitated by EF-G in prokaryotes and eEF2 in eukaryotes.

Termination

The translation process is terminated when a stop codon is encountered at the A site (UAG, UGA, or UAA), signaling the end of protein synthesis of the protein in question.

In prokaryotes, release factors release factor 1 or 2 (RF1 or RF2) recognize the stop codon, while eukaryotes rely on the eukaryotic release factor 1 and 3 (eRF1/eRF3)-GTP complex to bind the A-site. These factors induce hydrolysis of the bond between the polypeptide chain and the tRNA at the P-site, releasing the synthesized protein and disassembling the ribosome.

The genetic code

The genetic code is a nearly universal triple-nucleotide system that stands for the sequence of amino acids specified by the DNA-encoded mRNA into amino acid sequences of proteins through tRNAs and various factors. Along with transcription, this forms the central dogma of molecular biology.

The codon wheel or codon chart illustrates how nucleotide triplets determine amino acid sequences, with pyrimidines (T, U, C) and purines (A, G) organized into specific quadrants.

Key points of the genetic code in humans:

• Start Codon: AUG (Methionine)
• Stop Codons: UAA, UAG, UGA
• Each codon consists of three RNA bases (A, U, C, G)
• Multiple codons can encode the same amino acid (redundancy)

Each cell in the row-and-column codon chart represents a distinct codon and the amino acid it codes for. When using the chart, the relevant nucleotide on the table is found after the first letter of the codon has been determined. To identify the correct amino acid or the stop codon, we then go to the second and third letters of the codon.

Role of codons in protein synthesis

A codon is a set of three nucleotides (triplet) that functions as instructions for the cell, signaling when to start or stop the translation process and guiding the addition of specific amino acids to a growing polypeptide chain. For instance, in eukaryotes:

• The AUG codon signals the initiation of protein synthesis, while in prokaryotes, AUG, GUG, and UUG have also been reported.
• UAG, UAA, and UGA codons indicate termination of translation.
• The RNA-specific codon GCA instructs the addition of the amino acid alanine.

How tRNA decodes mRNA sequences

The transfer RNA  functions as an adaptor between the mRNA and ribosome.  tRNA recognizes specific codons on the mRNA through its complementary anticodon loop, ensuring the correct amino acid is added to the growing polypeptide chain.

The anticodon on tRNA pairing at the first two nucleotides of the triplet with the codon on mRNA is governed by base-pairing rules, and there is some flexibility in the third codon position. This is known as wobble base pairing or the wobble effect. This pairing process allows some tRNAs to recognize multiple codons.

This precise decoding mechanism, aided by aminoacyl-tRNA synthetases that charge tRNA with the correct amino acid, ensures the fidelity of protein synthesis while maintaining efficiency through the genetic code’s redundancy.

How replication, transcription, and translation work together

DNA replication, transcription, and translation work together to ensure that genetic information is accurately copied, expressed, and utilized to produce proteins essential for cellular functions.

• Replication: The first step in this sequence is DNA replication, where the entire genome is copied. This ensures that each new cell receives an identical set of genetic instructions. DNA replication occurs during the S phase of the cell cycle and is vital for maintaining genetic consistency across generations of cells.
• Transcription: Once DNA has been replicated, transcription takes place. This process involves the synthesis of messenger RNA (mRNA) from a specific segment of DNA. RNA polymerase reads the DNA template strand and produces an mRNA copy, which serves as a temporary, mobile version of the genetic code. Transcription occurs in the cell’s nucleus in eukaryotes, while in prokaryotes, it takes place in the cytoplasm.
• Translation: After transcription, the mRNA moves from the nucleus (in eukaryotes) to the cytoplasm, where translation occurs. In translation, ribosomes read the mRNA sequence and use it to assemble amino acids into proteins. Transfer RNA (tRNA) molecules bring the appropriate amino acids, and the ribosome links them together in the correct order based on the mRNA code.

Post-translational modifications

Post-translational modifications (PTMs) are chemical changes that alter the structure and function, and stability of proteins. These modifications are vital as they transform newly synthesized proteins into fully functional forms, enabling them to perform several roles in the cell.

Types of modifications proteins undergo

Here are some of the common PTMs for proteins.

• Phosphorylation - The addition of a phosphate group to hydroxyl (-OH) containing amino acids like serine, threonine, or tyrosine residues, and plays a key role in signal transduction. For instance, hyperphosphorylation of the Tau protein is higher in Alzheimer’s disease patients.
• Methylation - The addition of a methyl group to amino acids like lysine or arginine, particularly to histone proteins, often affects gene expression and chromatin structure.
• Acetylation: The addition of an acetyl group to lysine residues influences protein stability, function, and gene regulation. This may help in silencing or activating the gene. Acetylation plays a role in regulating cell metabolism and is associated with a variety of diseases, including cancer, cardiovascular disease, liver health, and neurological health.
• Glycosylation:  The attachment of sugar molecules to asparagine or serine/threonine residues, essential for protein folding and cell signaling.
• Ubiquitination: Addition of ubiquitin (Ub) chains, targeting them for degradation by the proteasome or altering their cellular roles.
• Lipidation: Attachment of lipid groups, such as fatty acids, to proteins, aiding in membrane localization and signaling.
• Redox modifications: These include altering the oxidation states (from −2 to +6) of sulfur in cysteine to facilitate bond formation.
• Sumolyation: It is the attachment of small Ub‐like modifiers (SUMOs) to lysine residues. This PTM is a subject of extensive research, given its role in aging, the development of tissues, and cellular control.
• Other modifications include carbamylation, citrullination, benzoylation, neddylation, etc.

PTMs regulate a wide range of processes, such as enzyme activation, signal transduction, and protein stability, ensuring proper cellular function and adaptation to environmental changes. Thus, it plays an important role in maintaining protein function and stability.

Visualizing DNA transcription and translation

Recent advances in single-molecule and single-cell techniques have provided powerful tools for studying transcription at high molecular resolution.

Techniques like fluorescence-based microscopy, optical tweezers, magnetic tweezers, and atomic force microscopy (AFM) allow researchers to explore various aspects of transcription, such as RNAP binding, translocation, mechanical forces, and DNA structural changes.

For live-cell studies, methods like single-molecule FISH, seqFISH+, and MS2/PP7 tagging enable real-time visualization of RNA synthesis. Further, in vitro, single-molecule methods remain essential for understanding detailed transcription mechanisms.

DNA coloring and interactive learning tools

DNA coloring and interactive learning tools allow users to visually explore and manipulate DNA structures. This helps in enhancing our understanding of genetic sequences and molecular interactions. These tools also provide an engaging, hands-on approach to studying DNA, making complex biological concepts more accessible and interactive.

NFkB p52 transcription factor assay kit is a colorimetric assay to quantify NF kappa beta (NFkB) in nuclear samples.

Benefits of visualization for complex processes

Visualization plays a vital role in simplifying complicated biological processes by presenting information in clear, visual formats that transform abstract ideas into more accessible and understandable forms.

For example - DNAproDB is a web-based interactive tool that helps researchers study DNA–protein complexes by processing structural features from these complexes and organizing the data for easy access. The tool offers customizable visualization tools for analyzing and creating high-quality figures of the DNA–protein interface, enabling users to search the database or upload their own structures for private analysis.

Photoactivatable fluorescent proteins (PA-FPs) attached to target molecules are used in photo-activated localization microscopy (PALM) to visualize transcription and translation at the nanoscale.

The PALM imaging process involves labeling the target proteins involved in transcription or translation through fusion with PA-FPs, facilitating specific visualization. For visualization, a low-intensity activation light selectively switches a random, sparse subset of PA-FPs from a dark to a fluorescent state. These fluorescent proteins are imaged until they photobleach. At any given time, only a small subset of these fluorophores are activated, allowing the imaging system to locate each molecule accurately by capturing its diffraction-limited spot.

PALM provides high-resolution images of transcriptional and translational machinery by repeatedly performing this activation process and precisely localizing and sequentially activating specific molecules over multiple cycles. PALM has several applications in transcription and translation studies, including identifying the location of RNA polymerase on DNA, visualizing the movement and interactions of transcription factors with DNA, mapping ribosomal localization on mRNA, identifying protein-protein interactions between transcription and translation machinery components, and subcellular compartmentalization. Another example is RNAscape, which helps visualize the tertiary and complex interaction of RNA molecules.

Applications of transcription and translation in biotechnology

Recent advances in spatially resolved transcriptomics have significantly enhanced the understanding of complex biological systems, with various new technologies emerging to combine gene expression data with spatial information.

• Transcription and translation are essential in genetic engineering for precise control over gene expression and the creation of synthetic genetic circuits.
• Techniques like CRISPR-dCas9, CRISPR-dCas13, and cell-free transcription-translation systems enable targeted gene editing and regulation, rapid prototyping, and testing of genetic networks. These approaches also expand biotechnological applications by characterizing genetic elements from non-model organisms.
• Transcription inhibitors target protein production in different cells, like cancerous cells. The advances in transcription factor design enable therapies like T-cell treatments. Primary antibodies like anti-PTF1A antibodies are used in immunohistochemistry and western blotting techniques.
• Engineered transcription systems provide precise gene regulation and enhance metabolite production in synthetic biology. Gene therapies and antiviral drugs leverage transcription insights to control gene expression and target mechanisms of pathogens.

FAQs

What role does RNA polymerase play in transcription?

RNA polymerase is responsible for synthesizing RNA from the DNA template by adding complementary RNA nucleotides to the growing strand during transcription. The RNA polymerase complex binds to the DNA template, unwinds the double helix, and catalyzes the formation of RNA from the DNA molecule. RNA polymerase also plays an important role in proofreading the newly synthesized RNA strand to ensure accurate transcription.

How does the central dogma relate to DNA transcription and translation?

The central dogma of molecular biology is a theory that explains the flow of genetic information from DNA to RNA (transcription) and from RNA to proteins (translation). It highlights how DNA is transcribed into messenger RNA, which is then translated into proteins that perform many cellular functions.

What is DNA transcription and translation simplified?

DNA transcription is the process where a segment of DNA is copied into an RNA molecule, which carries the genetic data of the DNA. Translation is the process where the RNA code is used to produce proteins involving several molecules, which perform various functions in the cell.

References

1. Dong, Y., Sun, F., Ping, Z, et al. DNA storage: research landscape and future prospects. National science review. 7, 1092-1107 (2020).