RME1, A NEGATIVE REGULATOR OF MEIOSIS, IS ALSO A POSITIVE ACTIVATOR OF G(1) CYCLIN GENE-EXPRESSION

Control of G(1) cyclin expression in Saccharomyces cerevisiae is media ted primarily by the transcription factor SBF (Swi4/Swi6). In the abse nce of Swi4 and Swi6 cell viability is lost, but can be regained by ec topic expression of the G(1) cyclin encoding genes, CLN1 or CLN2, Here we demonstrate that the RME1 (regulator of meiosis) gene can also byp ass the normally essential requirement for SBF, RME1 encodes a zinc fi nger protein which is able to repress transcription of IME1 (inducer o f meiosis) and thereby inhibit cells from entering meiosis, We have fo und that expression of RME1 from a high copy number plasmid can specif ically induce CLN2 expression, Deletion of RME1 alone shows no discern ible effect on vegetative growth, however, deletion of RME1 in a swi6 Delta swi4(ts) strain results in a lowering of the non-permissive temp erature for viability, This suggests that Rme1 plays a significant but ancillary role to SBF in inducing CLN2 expression, We show that Rme1 interacts directly with the CLN2 promoter and have mapped the region o f the CLN2 promoter required for Rme1-dependent activation, Consistent with Rme1 having a cell cycle role in G(1), we have found that RME1 m RNA is synthesized periodically in the cell cycle, with maximum accumu lation occurring at the M/G(1) boundary, Thus Rme1 may act both to pro mote mitosis, by activating CLN2 expression, and prevent meiosis, by r epressing IME1 expression.