Studies on the in vitro phosphorylation of HSSB-p34 and -p107 by cyclin-dependent kinases: Cyclin-substrate interactions dictate the efficiency of phosphorylation Journal Article
| Authors: | Gibbs, E.; Pan, Z. Q.; Niu, H.; Hurwitz, J. |
| Article Title: | Studies on the in vitro phosphorylation of HSSB-p34 and -p107 by cyclin-dependent kinases: Cyclin-substrate interactions dictate the efficiency of phosphorylation |
| Abstract: | Cyclin-dependent kinases (Cdks) are required for cell cycle progression. Two potentially significant Cdk substrates in human cells are the human single-stranded binding protein (HSSB or RPA), which plays an essential role in DNA replication, repair, and recombination, and the tumor suppressor p107 which acts to negatively regulate cell growth. In this report we describe the in vitro phosphorylation of these two proteins by Cdks in an attempt to understand how cyclin-substrate interactions direct phosphorylation efficiencies. We show that cyclin A-Cdk2 efficiently phosphorylates the p34 subunit of HSSB (HSSB-p34) alone or as a part of the heterotrimeric complex. In contrast, cyclin E-Cdk2 that is active in phosphorylating histone H1, does not support the phosphorylation of the p34 subunit of HSSB. We provide evidence that this differential phosphorylation results from a specific interaction between HSSB-p34 and cyclin A, but not cyclin E. Thus the observed cell cycle-dependent phosphorylation of HSSB-p34 at the G1 to S transition is most likely catalyzed by cyclin A-Cdk2 initiated by the direct interaction between cyclin A and the HSSB-p34 subunit. These studies are consistent with our previous observation that p107, which directly binds cyclin A, is efficiently phosphorylated by cyclin A-Cdk2 but not cyclin B- associated kinases. Here we further demonstrate that cyclin A only complexes with p107 in its unphosphorylated form. These data suggest a catalytic mechanism by which Cdk acts: substrate targeting by a cyclin-substrate interaction followed by dissociation of the Cdk upon phosphate incorporation allowing the Cdk to become available for the next cycle of phosphorylation. |
| Keywords: | controlled study; protein phosphorylation; human cell; dna-binding proteins; cell growth; hela cell; phosphorylation; nuclear proteins; molecular sequence data; protein-serine-threonine kinases; substrate specificity; base sequence; binding protein; molecular interaction; catalysis; cycline; cyclin-dependent kinases; cyclins; cyclin dependent kinase; enzyme substrate complex; replication protein a; electrophoresis, polyacrylamide gel; dna-activated protein kinase; cdc2 protein kinase; humans; human; priority journal; article |
| Journal Title: | Journal of Biological Chemistry |
| Volume: | 271 |
| Issue: | 37 |
| ISSN: | 0021-9258 |
| Publisher: | American Society for Biochemistry and Molecular Biology |
| Date Published: | 1996-09-13 |
| Start Page: | 22847 |
| End Page: | 22854 |
| Language: | English |
| DOI: | 10.1074/jbc.271.37.22847 |
| PUBMED: | 8798463 |
| PROVIDER: | scopus |
| DOI/URL: | |
| Notes: | Article -- Export Date: 22 November 2017 -- Source: Scopus |
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