Tolerance of Sir1p/origin recognition complex-dependent silencing for enhanced origin firing at HMRa.
Tolerance of Sir1p/origin recognition complex-dependent silencing for enhanced origin firing at HMRa.
复制标题
Sir1p/起源识别复合物依赖性沉默的耐受性，以增强 HMRa 的起源发射。
DOI：
10.1128/mcb.26.5.1955-1966.2006
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
Fox,CatherineA
中科院分区：
文献类型：
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作者：
McConnell,KristopherH;Muller,Philipp;Fox,CatherineA
HMR-E沉默分子是一种DNA元件，它指导酿酒酵母中HMRalocus沉默染色质的形成。Sir1p是HMRa沉默染色质形成所需的四种SIR蛋白之一。Sir1p的功能是通过结合与HMR-E结合的起源识别复合体(ORC)，并招募其他SIR蛋白(Sir2p至-4p)。兽人还与分布在基因组中的成百上千个非沉默位点结合，将它们标记为复制起始点。HMR-E也作为复制起始点，但与基因组中的许多起始点相比，它在S阶段启动效率极低且时间较晚。解释这一观察结果的一个假设是，ORC在起源激发中的作用与它结合Sir1p和/或形成沉默染色质的作用是不相容的。在这里，我们研究了突变的HMR-E消音器以及稳健的复制起始点和HMR-E之间的融合，以实现HMR沉默、起始点激发和复制计时。HMR-E消音器本身和HMR-E内的起始激发可以显著增强，并且在其他正常的S时相期间HMR复制的时间提前，而依赖于SIR1的沉默没有显著减少。然而，尽管强大的起源/消音器融合对HMR-A有很好的沉默作用，但它们的效果明显不如包含HMR-E的天然ORC结合位点的类似消音器。
TheHMR-E silencer is a DNA element that directs the formation of silent chromatin at theHMRalocus inSaccharomyces cerevisiae. Sir1p is one of four Sir proteins required for silent chromatin formation atHMRa. Sir1p functions by binding the origin recognition complex (ORC), which binds toHMR-E, and recruiting the other Sir proteins (Sir2p to -4p). ORCs also bind to hundreds of nonsilencer positions distributed throughout the genome, marking them as replication origins, the sites for replication initiation.HMR-E also acts as a replication origin, but compared to many origins in the genome, it fires extremely inefficiently and late during S phase. One postulate to explain this observation is that ORC's role in origin firing is incompatible with its role in binding Sir1p and/or the formation of silent chromatin. Here we examined a mutantHMR-E silencer and fusions between robust replication origins andHMR-E forHMRasilencing, origin firing, and replication timing. Origin firing withinHMRaand from theHMR-E silencer itself could be significantly enhanced, and the timing ofHMRareplication during an otherwise normal S phase advanced, without a substantial reduction inSIR1-dependent silencing. However, although the robust origin/silencer fusions silencedHMRaquite well, they were measurably less effective than a comparable silencer containingHMR-E's native ORC binding site.