CHROMOSOMAL REPLICATION INITIATES AND TERMINATES AT RANDOM SEQUENCES BUT AT REGULAR INTERVALS IN THE RIBOSOMAL DNA OF XENOPUS EARLY EMBRYOS
CHROMOSOMAL REPLICATION INITIATES AND TERMINATES AT RANDOM SEQUENCES BUT AT REGULAR INTERVALS IN THE RIBOSOMAL DNA OF XENOPUS EARLY EMBRYOS
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DOI：
10.1002/j.1460-2075.1993.tb06140.x
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发表时间：
1993-12-01
期刊：
影响因子：
11.4
通讯作者：
MECHALI, M
中科院分区：
文献类型：
--
作者：
HYRIEN, O;MECHALI, M
我们分析了中囊胚转变之前非洲爪蟾胚胎中染色体核糖体 DNA (rDNA) 簇的复制。二维凝胶分析表明复制叉与核基质相关，如在分化细胞中一样，并且没有提供单链复制中间体（RI）的证据。在分析的每个限制性片段中都发现了气泡、简单叉和双 Y，这表明复制的启动和终止没有可检测到的序列特异性。结果量化和数学分析表明，rDNA 复制子平均复制时间为 7.5 分钟，长度为 9 - 12 kbp。这个时间接近于总的S期持续时间，并且这个复制子大小接近于在这个短的S期内可以从单个起点复制的DNA的最大长度。因此，我们推断：(i) 大多数 rDNA 起点必须在 S 期很快同步激活，并且 (ii) 起点必须均匀分布，以便在 S 期结束时没有一段染色体 DNA 未被复制。由于起源不是特定的序列，因此表明这种空间和暂时的一致起始模式与某些周期性染色质折叠相匹配，而染色质折叠本身不需要依赖于 DNA 序列。
We have analysed the replication of the chromosomal ribosomal DNA (rDNA) cluster in Xenopus embryos before the midblastula transition. Two-dimensional gel analysis showed that replication forks are associated with the nuclear matrix, as in differentiated cells, and-gave no evidence for single-stranded replication intermediates (RIs). Bubbles, simple forks and double Ys were found in each restriction fragment analysed, showing that replication initiates and terminates without detectable sequence specificity. Quantification of the results and mathematical analysis showed that the average rDNA replicon replicates in 7.5 min and is 9 - 12 kbp in length. This time is close to the total S phase duration, and this replicon size is close to the maximum length of DNA which can be replicated from a single origin within this short S phase. We therefore infer that (i) most rDNA origins must be synchronously activated soon in S phase and (ii) origins must be evenly spaced, in order that no stretch of chromosomal DNA is left unreplicated at the end of S phase. Since origins are not specific sequences, it is suggested that this spatially and temporary concerted pattern of initiation matches some periodic chromatin folding, which itself need not rely on DNA sequence.