ANALYSIS OF REPLICATION ORIGIN FUNCTION ON CHROMOSOME-III OF SACCHAROMYCES-CEREVISIAE
ANALYSIS OF REPLICATION ORIGIN FUNCTION ON CHROMOSOME-III OF SACCHAROMYCES-CEREVISIAE
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DOI：
10.1101/sqb.1993.058.01.048
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发表时间：
1993-01-01
期刊：
影响因子：
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通讯作者：
THEIS, JF
中科院分区：
文献类型：
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作者：
NEWLON, CS;COLLINS, I;THEIS, JF
真核染色体含有长线性 DNA 分子，可在多个位点启动复制。尽管酿酒酵母的染色体 DNA 分子比多细胞真核生物的染色体 DNA 分子小两到三个数量级，但它们的复制模式相似，活性起点的间隔约为 40 kb（综述，参见 Newlon 1988），复制的时间顺序有规律（综述，参见 Fangman 和 Brewer 1991）。酵母在 DNA 复制研究中的一个重要优势是能够通过简单的质粒测定来识别潜在的染色体复制起点。这些自主复制序列 (ARS) 元件以顺式方式发挥作用，促进质粒的高频转化和染色体外维持（有关综述，请参阅 Campbell 和 New-Ion 1991）。我们对左侧端粒和右臂中部 MAT 基因座之间的 III 号染色体 200 kb 区域中的 ARS 元件进行分析（Newlon 等人，1986 年，1991 年），提出了许多问题。尽管分布不均匀，但所识别的 14 个 ARS 元件之间的平均间距约为 14 kb，仅为活动复制起点之间平均间距的三分之一。这种较短的间距可能反映了 III 号染色体上的起源密度高于整个基因组的起源密度。或者，某些 ARS 元件可能不具有作为染色体复制起点的活性，或者潜在的复制起点可能不会在每个细胞周期中启动复制。甚至活跃复制起点的平均密度似乎也远远高于所需的密度。根据测量的分叉运动速率和 S 期的平均长度，在 S 期早期启动的单个双向复制起点应该能够复制 120 kb 到 360 kb 的 DNA（有关审查，请参阅 Newlon 1988）。如果沿染色体存在复制叉障碍或染色体复制在 S 期晚期开始，则可能需要高密度的起点。或者，在正常的实验室生长条件下，复制起点可能是多余的。为了理解这些问题，我们进行了系统的研究
Eukaryotic chromosomes contain long linear DNA molecules that initiate replication at multiple sites. Although the chromosomal DNA molecules of the yeast Saccharomyces cerevisiae are two to three orders of magnitude smaller than those of multicellular eukaryotes, their replication pattern is similar, with active origins spaced at approximately 40-kb intervals (for review, see Newlon 1988) and a regular temporal order of replication (for review, see Fangman and Brewer 1991). An important advantage of yeast in the study of DNA replication is the ability to identify potential chromosomal origins of replication by a simple plasmid assay. These autonomously replicating sequence (ARS) elements act in cis to promote high-frequency transformation and the extrachromosomal maintenance of plasmids (for review, see Campbell and New-Ion 1991).Our analysis of ARS elements in the 200-kb region of chromosome III between the left telomere and the MAT locus in the middle of the right arm (Newlon et al. 1986, 1991) raised a number of questions. Although they are not uniformly distributed, the average spacing between the 14 ARS elements identified is approximately 14 kb, only one-third of the average spacing between active replication origins. This shorter spacing could reflect a higher density of origins on chromosome III than in the genome as a whole. Alternatively, some ARS elements might not be active as chromosomal replication origins, or potential replication origins might not initiate replication in every cell cycle. Even the average density of active replication origins seems considerably higher than necessary. Based on measured rates of fork movement and the average length of S phase, a single bidirectional replication origin that initiates early in S phase should be able to replicate between 120 kb and 360 kb of DNA (for review, see Newlon 1988). A high density of origins could be required if there were replication fork barriers along the chromosome or if replication of the chromosome initiated late in S phase. Alternatively, replication origins might be redundant under normal laboratory growth conditions. As an approach to understanding these questions, we have undertaken a systematic study