McCune Heather J, Danielson Laura S, Alvino Gina M, Collingwood David, Delrow Jeffrey J, Fangman Walton L, Brewer Bonita J, Raghuraman M K
Department of Genomic Resources, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA.
Genetics. 2008 Dec;180(4):1833-47. doi: 10.1534/genetics.108.094359. Epub 2008 Oct 1.
Temporal regulation of origin activation is widely thought to explain the pattern of early- and late-replicating domains in the Saccharomyces cerevisiae genome. Recently, single-molecule analysis of replication suggested that stochastic processes acting on origins with different probabilities of activation could generate the observed kinetics of replication without requiring an underlying temporal order. To distinguish between these possibilities, we examined a clb5Delta strain, where origin firing is largely limited to the first half of S phase, to ask whether all origins nonspecifically show decreased firing (as expected for disordered firing) or if only some origins ("late" origins) are affected. Approximately half the origins in the mutant genome show delayed replication while the remainder replicate largely on time. The delayed regions can encompass hundreds of kilobases and generally correspond to regions that replicate late in wild-type cells. Kinetic analysis of replication in wild-type cells reveals broad windows of origin firing for both early and late origins. Our results are consistent with a temporal model in which origins can show some heterogeneity in both time and probability of origin firing, but clustering of temporally like origins nevertheless yields a genome that is organized into blocks showing different replication times.
人们普遍认为，起始点激活的时间调控可以解释酿酒酵母基因组中早期和晚期复制区域的模式。最近，对复制的单分子分析表明，作用于具有不同激活概率的起始点的随机过程可以产生观察到的复制动力学，而无需潜在的时间顺序。为了区分这些可能性，我们研究了一个clb5Delta菌株，其中起始点的激发主要限于S期的前半段，以询问是否所有起始点都非特异性地显示激发减少（如无序激发所预期的那样），或者是否只有一些起始点（“晚期”起始点）受到影响。突变基因组中大约一半的起始点显示复制延迟，而其余的则基本按时复制。延迟区域可以涵盖数百千碱基，并且通常对应于野生型细胞中晚期复制的区域。对野生型细胞中复制的动力学分析揭示了早期和晚期起始点的广泛起始窗口。我们的结果与一个时间模型一致，在该模型中，起始点在起始时间和概率上都可以表现出一些异质性，但时间上相似的起始点的聚集仍然产生一个基因组，该基因组被组织成显示不同复制时间的区域。
