EUKARYOTIC CHROMOSOME REPLICATION

真核细胞染色体的复制是一个有序的过程，包括 在不同时间激活多组复制起始点 S阶段。激活每个复制点上的多个复制点 染色体确保每条染色体在每个细胞周期内复制。 一种特别严格的监管机制可以防止第二次激活 起源，从而防止染色体失衡。了解细胞如何 实施这些控制将需要更多关于规则的信息 它们控制着体内的起源激活。我们对酵母菌的研究 酿酒酵母已经开始揭示其中的一些规律。 我们建议检查四个控制复制来源的领域 激活。 (1)将原点放置在较近的位置会导致其 效率和可分配的非原点序列会影响哪个原点 激活了。我们将测试模型的干扰并确定 偏向原产地选择的机制。 (2)与端粒的接近导致起始点的激活 推迟到S后期。我们将决定是否维护 “晚期上下文”要求端粒连续的物理连接到 染色体，当处于细胞周期时，上下文就建立起来了。 (3)早期起始激活可被非端粒、顺式- 独立于端粒的作用元件。我们将描述 元素，并使用它来确定更改计时对 染色体稳定性。我们将定义后期复制域的大小。 (4)真核生物的染色体起源似乎仅限于 基因间DNA。利用酿酒酵母和拟南芥，我们将测试 假设启动被限制在基因间序列中，通过 基因边界的性质。 这项工作将使人们对监管有更深的理解 正常细胞和生长缺陷细胞的染色体复制 属性，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.