• Nature
  • Source
    Escherichia coli
  • Amino Acid Sequence
    • Species
    • Tags
      GST tag N-Terminus


Our Abpromise guarantee covers the use of ab56278 in the following tested applications.

The application notes include recommended starting dilutions; optimal dilutions/concentrations should be determined by the end user.

  • Applications

    Functional Studies


    Western blot

  • Form
  • Concentration information loading...

Preparation and Storage

  • Stability and Storage

    Shipped on dry ice. Upon delivery aliquot and store at -80ºC. Avoid freeze / thaw cycles.

    pH: 7.50
    Constituents: 0.0038% EGTA, 0.00174% PMSF, 0.00385% DTT, 0.79% Tris HCl, 0.00292% EDTA, 25% Glycerol, 0.87% Sodium chloride

General Info

  • Alternative names
    • CAP20
    • CDK-interacting protein 1
    • CDKI
    • CDKN1
    • Cdkn1a
    • CIP1
    • Cyclin Dependent Kinase Inhibitor 1A
    • Cyclin-dependent kinase inhibitor 1
    • Cyclin-dependent kinase inhibitor 1A (P21)
    • Cyclin-dependent kinase inhibitor 1A (p21, Cip1)
    • DNA Synthesis Inhibitor
    • MDA-6
    • MDA6
    • Melanoma differentiation-associated protein
    • Melanoma differentiation-associated protein 6
    • p21
    • P21 protein
    • p21CIP1
    • p21Cip1/Waf1
    • p21WAF
    • PIC1
    • SDI1
    • SLC12A9
    • WAF1
    • Wild type p53 activated fragment 1
    • Wild type p53 activated fragment 1 (WAF1)
    • Wildtype p53-activated fragment 1
    see all
  • Function
    May be the important intermediate by which p53/TP53 mediates its role as an inhibitor of cellular proliferation in response to DNA damage. Binds to and inhibits cyclin-dependent kinase activity, preventing phosphorylation of critical cyclin-dependent kinase substrates and blocking cell cycle progression. Functions in the nuclear localization and assembly of cyclin D-CDK4 complex and promotes its kinase activity towards RB1. At higher stoichiometric ratios, inhibits the kinase activity of the cyclin D-CDK4 complex.
  • Tissue specificity
    Expressed in all adult human tissues, with 5-fold lower levels observed in the brain.
  • Sequence similarities
    Belongs to the CDI family.
  • Domain
    The PIP-box K+4 motif mediates both the interaction with PCNA and the recuitment of the DCX(DTL) complex: while the PIP-box interacts with PCNA, the presence of the K+4 submotif, recruits the DCX(DTL) complex, leading to its ubiquitination.
    The C-terminal is required for nuclear localization of the cyclin D-CDK4 complex.
  • Post-translational
    Phosphorylation of Thr-145 by Akt or of Ser-146 by PKC impairs binding to PCNA. Phosphorylation at Ser-114 by GSK3-beta enhances ubiquitination by the DCX(DTL) complex.
    Ubiquitinated by MKRN1; leading to polyubiquitination and 26S proteasome-dependent degradation. Ubiquitinated by the DCX(DTL) complex, also named CRL4(CDT2) complex, leading to its degradation during S phase or following UV irradiation. Ubiquitination by the DCX(DTL) complex is essential to control replication licensing and is PCNA-dependent: interacts with PCNA via its PIP-box, while the presence of the containing the 'K+4' motif in the PIP box, recruit the DCX(DTL) complex, leading to its degradation.
  • Cellular localization
    Cytoplasm. Nucleus.
  • Information by UniProt


  • Standard curve for p21 (Analyte: ab56278); dilution range 1pg/ml to 1µg/ml using Capture Antibody Mouse monoclonal [AC8.3] to p21 (ab118) at 5µg/ml and Detector Antibody Rabbit polyclonal to p21 (ab18209) at 0.5µg/ml.
  • SDS-PAGE analysis of ab56278 with molecular weight markers. Approximate molecular weight 46kDa.


This product has been referenced in:
  • Sun Z  et al. Increased SHP-1 expression results in radioresistance, inhibition of cellular senescence, and cell cycle redistribution in nasopharyngeal carcinoma cells. Radiat Oncol 10:152 (2015). Read more (PubMed: 26215037) »
See 1 Publication for this product

Customer reviews and Q&As

1-3 of 3 Abreviews or Q&A


Thank you for contacting Abcam regarding ab56278.

Regarding this p21 protein, the isoelectric point has not been determined. Currently we do not have a service for custom conjugation of proteins, however, we do sell simple 3 step kits that can be used to conjugate the protein yourself.

I would like to recommend the FITC EasyLink Conjugation kit, ab102885 along with the Purification kit ab102784 to clean up the protein buffer.

I hope this information is helpful. Please do not hesitate to contact me if you have any additional questions.

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Thanks again for your email and for your patience.

I've heard back from my colleagues in the lab, and the GST tag can be cleaved using a thrombin digestion protocol. We don't have a suggested digestion protocol, but there are many available online such as-


I hope this information will be useful, but please let me know if there is anything else that we can do for you and I'll be happy to help.

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Thank you for contacting us with your question about ab56278.

This p21 proteincontains an N-terminal GST tag. Ihave contactedthe production labto requestmore information about a protocol to remove the GST, and I'll get back to you as soon as I have this information.

Please let me know if you have any other questions in the meantime or if there is anything else that we can do for you.

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