CDI-1-MEDIATED REPRESSION OF CELL-CYCLE GENES TARGETS A SPECIFIC SUBSET OF TRANSACTIVATORS

The cdc25C, cyclin A and cdc2 genes are regulated during the cell cycl e through two contiguous repressor binding sites, the CDE and CHR, loc ated in the region of transcription initiation and interacting with a factor termed CDF-1. The target of this repression seems to be transcr iptional activation of these promoters by transcription factors bound upstream, The majority of these factors falls into the class of glutam ine-rich activators, suggesting that CDF-1-mediated repression might b e activation domain specific, In the present study we have used chimer ic promoter constructs to demonstrate that the cdc25C UAS, but not the core promoter, is crucial for repression, In addition, we show that o nly specific transcription factors and activation domains are responsi ve to CDE-CHR-mediated cell cycle regulation, These observations clear ly indicate that CDF-1 interferes with activation of transcription by a specific subset of transactivators, The repressible activation domai ns belong to the same class of glutamine-rich activators, pointing to specific interactions of CDF-1 with components of the transcription ma chinery. In agreement with this conclusion we find that a simple inver sion of the CDE-CHR module completely abrogates cell cycle-regulated r epression.