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首页> 美国卫生研究院文献>Molecular and Cellular Biology >Activation of Silent Replication Origins at Autonomously Replicating Sequence Elements near the HML Locus in Budding Yeast
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Activation of Silent Replication Origins at Autonomously Replicating Sequence Elements near the HML Locus in Budding Yeast

机译：在萌发酵母中HML基因座附近的自主复制序列元件处激活无声复制起点。

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摘要

In the budding yeast, Saccharomyces cerevisiae, replicators can function outside the chromosome as autonomously replicating sequence (ARS) elements; however, within chromosome III, certain ARSs near the transcriptionally silent HML locus show no replication origin activity. Two of these ARSs comprise the transcriptional silencers E (ARS301) and I (ARS302). Another, ARS303, resides between HML and the CHA1 gene, and its function is not known. Here we further localized and characterized ARS303 and in the process discovered a new ARS, ARS320. Both ARS303 and ARS320 are competent as chromosomal replication origins since origin activity was seen when they were inserted at a different position in chromosome III. However, at their native locations, where the two ARSs are in a cluster with ARS302, the I silencer, no replication origin activity was detected regardless of yeast mating type, special growth conditions that induce the transcriptionally repressed CHA1 gene, trans-acting mutations that abrogate transcriptional silencing at HML (sir3, orc5), or cis-acting mutations that delete the E and I silencers containing ARS elements. These results suggest that, for the HML ARS cluster (ARS303, ARS320, and ARS302), inactivity of origins is independent of local transcriptional silencing, even though origins and silencers share key cis- and trans-acting components. Surprisingly, deletion of active replication origins located 25 kb (ORI305) and 59 kb (ORI306) away led to detection of replication origin function at the HML ARS cluster, as well as at ARS301, the E silencer. Thus, replication origin silencing at HML ARSs is mediated by active replication origins residing at long distances from HML in the chromosome. The distal active origins are known to fire early in S phase, and we propose that their inactivation delays replication fork arrival at HML, providing additional time for HML ARSs to fire as origins.
机译：在萌芽的酿酒酵母中，复制子可以在染色体外作为自主复制序列（ARS）元件起作用。但是，在染色体III中，转录沉默HML基因座附近的某些ARS没有复制起点活性。这些ARS中的两个包含转录沉默子E（ARS301）和I（ARS302）。另一个是ARS303，位于HML和CHA1基因之间，其功能尚不清楚。在这里，我们进一步对ARS303进行了定位和表征，并在此过程中发现了新的ARS，即ARS320。 ARS303和ARS320都可以作为染色体复制起点，因为在将它们插入第III染色体的不同位置时看到了起点活性。但是，在两个ARS与IRS ARS302簇聚的天然位置，无论酵母的交配类型，诱导转录抑制的CHA1基因的特殊生长条件，反式突变都没有检测到复制起点活性。在HML（sir3， orc5 ）或 cis 作用突变中消除转录沉默，这些突变删除包含ARS元素的E和I沉默子。这些结果表明，对于 HML ARS群集（ ARS303 ， ARS320 和 ARS302 ），起源不活跃即使起源和沉默子共享关键的 cis -和 trans 作用元件，它也独立于局部转录沉默。令人惊讶的是，删除了分别位于25 kb（ORI305）和59 kb（ORI306）之外的主动复制起点，导致在 HML ARS群集以及 ARS301 上检测到复制起点功能em>，E消音器。因此，在 HML ARS处的复制起点沉默是由与染色体中 HML 较远距离的主动复制起点介导的。远端活动起源已知在S期早期触发，我们建议其失活会延迟复制叉到达 HML 的时间，从而为 HML ARS触发提供更多时间。

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