Identification of the active region of the DNA synthesis inhibitory gene P21Sdi1/CIP1/WAF1

Makoto Nakanishi, Ryan S. Robetorye, Guy R. Adami, Olivia M. Pereira-Smith, James R. Smith

Research output: Contribution to journalArticlepeer-review

168 Scopus citations


The cloning of the negative growth regulatory gene, p21sdi1, has led to the convergence of the fields of cellular senescence, cell cycle regulation and tumor suppression. This gene was first cloned as an inhibitor of DNA synthesis that was overexpressed in terminally non-dividing senescent human fibroblasts (SDI1) and later as a p53 transactivated gene (WAF1) and a Cdk-interacting protein (CIP1, p21) that inhibited cyclin-dependent kinase activity. To identify the active region(s) of p21Sdi1, cDNA constructs encoding various deleted forms of the protein were analyzed. Amino acids 22-71 were found to be the minimal region required for DNA synthesis inhibition. Amino acids 49-71 were involved in binding to Cdk2, and constructs deleted in this region expressed proteins that were unable to inhibit Cdk2 kinase activity in vitro. The latter stretch of amino acids shared sequence similarity with amino acids 60-76 of the p21Kip1 protein, another Cdk inhibitor. Point mutations made in p21Sdi1 in this region confirmed that amino acids common to both proteins were involved in DNA synthesis inhibition. Additionally, a chimeric protein, in which amino acids 49-65 of p21sdil were substituted with amino acids 60-76 of p27Kip1, had almost the same DNA synthesis inhibitory activity as the wild-type protein. The results indicate that the region of sequence similarity between p21sdi1 and p27Kip1 encodes an inhibitory motif characteristic of this family of Cdk inhibitors.

Original languageEnglish (US)
Pages (from-to)555-563
Number of pages9
JournalEMBO Journal
Issue number3
StatePublished - Feb 1 1995


  • Cdk
  • Cell cycle
  • Proliferation
  • Sdi1
  • p21

ASJC Scopus subject areas

  • General Neuroscience
  • Molecular Biology
  • General Biochemistry, Genetics and Molecular Biology
  • General Immunology and Microbiology


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