Specific association of cyclin-like uracil-DNA glycosylase with the proliferating cell nuclear antigen

We have previously isolated a human gene that encodes a cyclin-like protein with uracil-removing activity (UDG2) (Muller, S.J., and Caradonna, S. 1993. J. Biol. Chem. 268, 1310-1319). The structural and regulatory similarities shared between this uracil-DNA glycosylase and cyclins suggested that it may interact with additional proteins. Using a unique affinity purification protocol (Ugi-Sepharose) and anti-UDG2 antibodies, we have identified a physical interaction between the cyclin-like uracil-DNA glycosylase and PCNA in extracts derived from HeLa cells. Conversely, we show that anti-PCNA immunoprecipitates possess significant uracil-DNA glycosylase activity. This activity is specifically blocked by the addition of uracil-DNA glycosylase inhibitor protein (Ugi) derived from bacteriophage PBS2. To further characterize this association, we performed in vitro mixing experiments using 35S-labeled PCNA and uracil-DNA glycosylase (UDG2) that were generated in a coupled transcription/translation system. We show that UDG2 and PCNA are coprecipitated using anti-PCNA antibodies and anti-UDG2 antibodies as well as Ugi-Sepharose. When PCNA is preincubated with synthetic peptides corresponding to amino acid residues 73-90 of UDG2, the PCNA-UDG2 association is prevented. By contrast, addition of synthetic peptides corresponding to amino acid residues 208-223 has no effect on this interaction. These findings suggest that the UDG2 domain encompassing amino acids 73-90 is directly involved in binding PCNA.