Sakakibara Y
Department of Chemistry, National Institute of Health, Tokyo, Japan.
J Mol Biol. 1992 Aug 20;226(4):989-96. doi: 10.1016/0022-2836(92)91047-s.
A new Escherichia coli mutant named dnaR, which was temperature sensitive in initiation of DNA replication, has been characterized through identification of the mutant gene. A 1.65 x 10(3) base-pair chromosomal DNA fragment isolated from wild-type cells, but not the corresponding fragment from the dnaR mutant, exhibited an activity that reversed temperature-sensitive growth of the mutant. The DNA fragment was found to include the entire prs-coding sequence and specify a 34,000 M(r) protein with phosphoribosylpyrophosphate synthetase activity. The dnaR mutation resided within the prs-coding segment and made the synthetase thermolabile. The coding segment for the dnaR product was determined, by introduction of various mutations into the cloned fragment, to be the same as that for the synthetase. The dnaR function of the prs gene product in DNA replication is discussed on the basis of an observation that thermal treatment of the dnaR mutant caused a delay in initiation of chromosome replication after the downshift, despite the presence of the synthetase activity at the preheat level.
一种名为dnaR的新型大肠杆菌突变体，其在DNA复制起始方面对温度敏感，已通过对突变基因的鉴定进行了表征。从野生型细胞中分离出的一个1.65×10³碱基对的染色体DNA片段，而不是来自dnaR突变体的相应片段，表现出一种能逆转该突变体温度敏感生长的活性。发现该DNA片段包含整个prs编码序列，并指定一种具有磷酸核糖焦磷酸合成酶活性的34,000 M（r）蛋白质。dnaR突变位于prs编码区段内，使合成酶对热不稳定。通过将各种突变引入克隆片段，确定dnaR产物的编码区段与合成酶的编码区段相同。基于对dnaR突变体进行热处理后，尽管在预热水平存在合成酶活性，但在温度下降后染色体复制起始延迟这一观察结果，讨论了prs基因产物的dnaR功能在DNA复制中的作用。
