Iwasaki H, Ishino Y, Toh H, Nakata A, Shinagawa H
Department of Experimental Chemotherapy, Osaka University, Japan.
Mol Gen Genet. 1991 Apr;226(1-2):24-33. doi: 10.1007/BF00273583.
The Escherichia coli polB gene encodes DNA polymerase II and is regulated by the SOS system. We sequenced a 4081 nucleotide segment of the E. coli chromosome that contains the polB gene and its flanking regions. DNA polymerase II, as deduced from the DNA sequence, consists of 782 amino acids, has a molecular weight of 89,917, and is structurally homologous to alpha-like DNA polymerases, which include eukaryotic replicative DNA polymerases. Comparison of the sequences of the alpha-like DNA polymerases including E. coli DNA polymerase II showed that there were nine highly conserved regions, and we constructed an unrooted phylogenetic tree of the DNA polymerases based on the differences in these conserved regions. The DNA polymerases of herpes groups viruses and the DNA polymerases that use protein priming for the initiation of replication form two separate subfamilies that occupy opposite locations in the tree. Other DNA polymerases, including E. coli DNA polymerase II, human DNA polymerase alpha, and yeast DNA polymerase I, occupy the central regions between the two subfamilies and they are rather distantly related to each other. The transcription initiation site of polB was identified by analysis of in vivo transcripts, and the promoter was assigned upstream of the polB coding region. The recognition sequence of the LexA repressor (SOS box) was identified by a footprinting experiment. It overlaps the -35 sequence of the polB promoter.
大肠杆菌polB基因编码DNA聚合酶II，并受SOS系统调控。我们对大肠杆菌染色体上一段包含polB基因及其侧翼区域的4081个核苷酸片段进行了测序。从DNA序列推导得出的DNA聚合酶II由782个氨基酸组成，分子量为89917，在结构上与α类DNA聚合酶同源，其中包括真核生物复制性DNA聚合酶。对包括大肠杆菌DNA聚合酶II在内的α类DNA聚合酶序列进行比较后发现有九个高度保守区域，我们基于这些保守区域的差异构建了DNA聚合酶的无根系统发育树。疱疹病毒群的DNA聚合酶以及利用蛋白质引发复制起始的DNA聚合酶形成了两个独立的亚家族，它们在树中占据相对的位置。其他DNA聚合酶，包括大肠杆菌DNA聚合酶II、人类DNA聚合酶α和酵母DNA聚合酶I，占据了这两个亚家族之间的中心区域，并且它们彼此之间的关系较为疏远。通过对体内转录本的分析确定了polB的转录起始位点，并将启动子定位在polB编码区的上游。通过足迹实验确定了LexA阻遏物的识别序列（SOS框）。它与polB启动子的 -35序列重叠。
