CONTROL OF S-PHASE PERIODIC TRANSCRIPTION IN THE FISSION YEAST MITOTIC-CYCLE

In fission yeast, passage through START and into S-phase requires cycl in-dependent kinase (CDK) activity and the periodic transcription of g enes essential for S-phase ('S-phase transcription'). Here we investig ate the control of this transcription in the mitotic cell cycle, We de monstrate that the periodicity of S-phase transcription is likely to b e controlled independently of CDK activity, This contrasts with the eq uivalent system in budding yeast, Furthermore, the CDK function requir ed for S-phase acts after the onset of S-phase transcription and after the accumulation of cdc18p. a critical target of this transcriptional machinery, We investigate the role of individual components of the S- phase transcriptional machinery, cdc10p, res1p, res2p and rep2p, and d efine a new role for res2p, previously demonstrated to be important in the meiotic cycle, in switching off S-phase transcription during G2 o f the mitotic cycle, We show that the presence of the in vitro bandshi ft activity DSC1, conventionally thought to represent the active compl ex, requires res2p and correlates with inactive transcription, We sugg est that S-phase transcription is controlled by both activation and re pression, and that res2p represses transcription in G2 of the cell cyc le as a part of the DSC1 complex.