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Mol. Cell. Biol., 09 1996, 4673-4682, Vol 16, No. 9
J Chen, P Saha, S Kornbluth, BD Dynlacht and A Dutta
The cyclin-dependent kinase (Cdk) inhibitor p21 is induced by the tumor
suppressor p53 and is required for the G1-S block in cells with DNA damage.
We report that there are two copies of a cyclin-binding motif in p21, Cy1
and Cy2, which interact with the cyclins independently of Cdk2. The
cyclin-binding motifs of p21 are required for optimum inhibition of
cyclin-Cdk kinases in vitro and for growth suppression in vivo. Peptides
containing only the Cy1 or Cy2 motif partially inhibit cyclin-Cdk kinase
activity in vitro and DNA replication in Xenopus egg extracts. A monoclonal
antibody which recognizes the Cy1 site of p21 specifically disrupts the
association of p21 with cyclin E-Cdk2 and with cyclin D1-Cdk4 in cell
extracts. Taken together, these observations suggest that the
cyclin-binding motif of p21 is important for kinase inhibition and for
formation of p21-cyclin-Cdk complexes in the cell. Finally, we show that
the cyclin-Cdk complex is partially active if associated with only the
cyclin-binding motif of p21, providing an explanation for how p21 is found
associated with active cyclin-Cdk complexes in vivo. The Cy sequences may
be general motifs used by Cdk inhibitors or substrates to interact with the
cyclin in a cyclin-Cdk complex.
Copyright © 1996, American Society for Microbiology
Cyclin-binding motifs are essential for the function of p21CIP1
Department of Pathology, Division of Molecular Oncology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
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