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Mol. Cell. Biol., Dec 1996, 7173-7181, Vol 16, No. 12
KN Chow, P Starostik and DC Dean
Progression through the cell cycle is dependent on the sequential
expression of cyclins, which combine with cyclin-dependent kinases (cdks)
to form active kinases. The transition from G1 to S phase is dependent on D
cyclins in complex with cdk4 or cdk6 and cyclin E complexed with cdk2. One
target of G1 cyclins is the retinoblastoma susceptibility protein (Rb). Rb
is a transcriptional repressor that is selectively targeted to genes
through interaction with the E2F family of cell cycle transcription
factors. Rb is a member of a family of proteins that include p107 and p130.
The three proteins share a region known as the pocket that is important for
binding E2F and is also the binding site for oncoproteins from DNA tumor
viruses that inactivate Rb. We have found that two conserved domains within
the Rb pocket (A and B) interact to form a transcriptional repressor motif
(K. N. B. Chow and D. C. Dean, Mol. Cell. Biol. 16:4862-4868, 1996). Here
we demonstrate that p107 also has an A-B repressor motif, and using domain
swapping and coimmunoprecipitation assays, we compare A and B from Rb and
p107. Finally and most importantly, we demonstrate that the A-B interaction
which forms the repressor motif is blocked by G1 cdk phosphorylation,
thereby blocking repressor activity. This A-B repressor motif is then the
first example of a cdk-regulated transcriptional repressor.
Copyright © 1996, American Society for Microbiology
The Rb family contains a conserved cyclin-dependent-kinase-regulated transcriptional repressor motif
Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
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