D-TYPE CYCLIN-BINDING REGIONS OF PROLIFERATING CELL NUCLEAR ANTIGEN

Proliferating cell nuclear antigen (PCNA) is an auxiliary protein for DNA polymerase delta and is required for both DNA replication and DNA repair. PCNA forms complexes with D-type cyclins, candidate G1 cyclins in mammalian cells. To better understand the functions of the complex es, we examined interactions between PCNA and D-type cyclins, using in vitro-translated mouse PCNA and mouse cyclin D1 or D3 fused to glutat hione S-transferase (GST). Analysis of a set of deletion mutants of PC NA revealed that either the N-terminal (residues 2-64) or the C-termin al (residues 197-228) region is necessary for association with D-type cyclins. The cyclin binding of the chimeric protein of the N-terminal (residues 1-68) or the C-terminal (residues 195-261) region of PCNA an d rat DNA polymerase beta which does not bind to the cyclins by itself supports this notion. The purified recombinant mouse PCNA expressed i n Escherichia coli bound to the D-type cyclin-GST fusion proteins, the reby suggesting that PCNA binds directly to D-type cyclins, without th e requirement of other cellular factors. This is apparently the first report on the structure-function relationship of PCNA which may link D NA replication and DNA repair with cell cycle control.