Kato J, Nishimura Y, Yamada M, Suzuki H, Hirota Y
Department of Biology, Faculty of Science, University of Tokyo, Japan.
J Bacteriol. 1988 Sep;170(9):3967-77. doi: 10.1128/jb.170.9.3967-3977.1988.
A new mutation, parC, causing abnormal chromosome segregation was identified in two thermosensitive mutants of Escherichia coli. The thermosensitive growth of the mutants was corrected by pLC4-14 in the Clarke-Carbon collection. This plasmid carries a putative gene which can suppress the cell division defect due to ftsI (pbpB) and has hence been termed sufI (sui). The nearness of parC to metC was confirmed, and cotransduction frequency of parC was 59% with metC and 20% with glc. The parC-sufI region was analyzed by subcloning the chromosome region of pLC4-14. The parC and the sufI gene products were electrophoretically identified as proteins of 75 and 55 kilodaltons (kDa), respectively. The allelism of parC+ on pLC4-14 to parC1215 was confirmed by cloning parC1215. The sufI gene appeared to be dispensable for cell viability, and overproduction of its product caused suppression of ftsI. An essential gene coding for a 25-kDa protein was found between the parC and the sufI gene. These three genes were transcribed in the same direction and may be organized into an operon, with parC to the proximal side and with internal promoters at least for the distal genes. The localization of the gene products was examined in maxicells. The sufI protein was synthesized as a precursor which could be chased into a mature form. The major part of the mature form was found in the soluble fraction. The 25-kDa protein was found almost exclusively in the membrane fraction. The parC protein was associated with the membrane fraction in the presence of Mg2+ but found in the soluble fraction when Mg2+ was sequestered with EDTA.
在大肠杆菌的两个温度敏感型突变体中鉴定出一种导致染色体分离异常的新突变parC。在克拉克-卡尔本收集文库中的pLC4 - 14可纠正这些突变体的温度敏感型生长。该质粒携带一个假定基因，它可以抑制ftsI（pbpB）导致的细胞分裂缺陷，因此被命名为sufI（sui）。证实了parC与metC距离较近，parC与metC的共转导频率为59%，与glc的共转导频率为20%。通过亚克隆pLC4 - 14的染色体区域对parC - sufI区域进行了分析。电泳鉴定parC和sufI基因产物分别为75千道尔顿（kDa）和55千道尔顿的蛋白质。通过克隆parC1215证实了pLC4 - 14上的parC⁺与parC1215的等位性。sufI基因似乎对细胞活力并非必需，其产物的过量表达导致ftsI的抑制。在parC和sufI基因之间发现了一个编码25 kDa蛋白质的必需基因。这三个基因同向转录，可能组成一个操纵子，parC位于近端，至少远端基因有内部启动子。在大细胞中检测了基因产物的定位。sufI蛋白以前体形式合成，可追踪为成熟形式。成熟形式的大部分存在于可溶部分。25 kDa蛋白质几乎只存在于膜部分。parC蛋白在有Mg²⁺存在时与膜部分相关，但当用EDTA螯合Mg²⁺时则存在于可溶部分。
