IDENTIFICATION OF A P130 DOMAIN MEDIATING INTERACTIONS WITH CYCLIN-A CDK2 AND CYCLIN-E CDK2 COMPLEXES

P130 shares structural and functional homology with pRb and p107. One property common to p107 and p130, but not to pRb, is the ability to st ably interact with cyclin A/cdk2 and cyclin E/cdk2 complexes in vitro and in vivo. Using GST-p130 fusion proteins representing various regio ns of p130, baculovirus-produced cyclin A/ cdk2 and cyclin E/cdk2 comp lexes were found to interact with residues within a part of p130 known as the spacer region. Cyclin E was able to bind the p130 spacer regio n in the presence or absence of cdk2 whereas cyclin A binding was depe ndent upon the presence of cdk2. The smallest p130 fusion protein suff icient to interact with cyclin A/cdk2 or cyclin E/cdk2 complexes conta ined p130 amino acids 652-698 and deletion of p130 amino acids 680-682 abolished binding to both of the cyclin/cdk2 complexes. When overexpr essed in C33A cells, a p130 mutant containing a deletion of amino acid s 620-697 was unable to form complexes with either cyclin A or cyclin E. This p130 mutant was at least as active as wild type p130 in suppre ssing the growth of G418 resistant colonies when overexpressed in C33A or SAOS-2 cells.