Cooperation at a distance between silencers and proto-silencers at the yeast HML locus
Résumé
Transcriptional repression at the silent yeast mating typelociisachievedthroughtheformationofaparticu- lar nucleoprotein complex at specific cis-acting ele- ments called silencers. This complex in turn appears to initiate the spreading of a histone binding protein complex into the surrounding chromatin, which restrictsaccessibilityoftheregiontothetranscription machinery. We have investigated long-range, cooperative effects between silencers by studying the repressionofa reporter gene integratedattheHML locus flanked by various combinations of wild-type and mutated silencer sequences. Two silencers can cooperate over >4000 bp to repress transcription eficiently.More importantly,a singlebindingsitefor either the repressor activator protein 1 (Rapl), the autonomous replicating sequence (ARS) binding factor 1 (Abfl) or the origin recognition complex (ORC) can enhance the action of a distant silencer without acting as a silencer on its own. Functional cooperativity is demonstratedusingaquantitativeassayforrepression, and varies with the affinity of the binding sites used. Since the repression mechanism is Sir dependent, the Rapl, ORC and/or Abfl proteins bound to distant DNA elements may interact to create an interface of sufficiently high affinity such that Sir-containing complexes bind, nucleating the silent chromatin state.
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Boscheron et al. - 1996 - Cooperation at a distance between silencers and pr.pdf (2.73 Mo)
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