EUKARYOTIC CHROMOSOME REPLICATION

真核生物染色体的复制是一个有序的过程， 复制起始点在不同时间的激活， S期 每个细胞上多个复制起点的激活 染色体确保每个染色体在每个细胞周期中复制。 一种特别严格的调节机制可以防止第二次激活。 从而防止染色体不平衡。 了解细胞如何 实施这些控制将需要更多关于规则的信息 控制着体内的起源激活。 我们对酵母的研究 酿酒酵母已经开始揭示其中的一些规则。 我们建议检查复制起点控制的四个方面 activation. (1)将原点放置得很近， 效率，和必要的，非起源序列影响哪个起源是 激活 我们将测试模型的干扰， 偏向起源选择的机制。 (2)接近端粒导致一个起源的激活， 延迟至S期晚期。 我们将决定是否维持 “晚期背景”需要端粒连续的物理附着， 染色体和细胞周期中的背景建立。 (3)早期起源激活可以被非端粒的顺式- 独立于端粒的作用元件。 我们将描述 此元素，并使用它来确定更改的定时对 染色体稳定性 我们将定义后期复制域的大小。 (4)真核染色体起源似乎仅限于 基因间DNA 利用S.酿酒酵母和拟南芥，我们将测试 这一假说认为，启动被限制在基因间序列， 基因边界的性质。 这项工作将使人们更好地了解 正常细胞和生长缺陷细胞中的染色体复制 性质，如癌细胞。

Replication of the eukaryotic chromosome is an ordered process involving the activation of sets of replication origins at different times during the S phase. The activation of multiple replication origins on each chromosome insures that every chromosome replicates during each cell cycle. An especially rigorous regulatory mechanism prevents second activation of origins thereby preventing chromosome imbalance. Understanding how cells impose these controls will require much more information about the rules that govern origin activation in vivo. Our work with the yeast Saccharomyces cerevisae has begun to reveal some of these rules. We propose to examine four areas of control of replication origin activation. (1) Placing origins in close proximity results in reduction in their efficiency, and dispensible, non-origin sequences influence which origin is activated. We will test models for interference and determine the mechanism that biases origin selection. (2) The proximity to a telomere causes an origin's activation to be delayed until late S phase. We will determine whether maintenance of the "late-context" requires continuous physical attachment of the telomere to the chromosome and when in the cell cycle the context is established. (3) Early origin activation can be suppressed by a non-telomeric, cis- acting element that is independent of the telomere. We will characterize this element and use it to determine the effect of altered timing on chromosome stability. We will define the size of late replicating domains. (4) Eukaryotic chromosomal origins appear to be confined exclusively to intergenic DNA. Using S. cerevisiae and Arabidopsis thaliana we will test the hypothesis that initiations are confined to intergenic sequences by properties of gene boundaries. This work will lead to a greater understanding of the regulation of chromosome replication in normal cells and in those with defective growth properties, such as cancer cells.