Nohmi T, Yamada M, Matsui K, Watanabe M, Sofuni T
Division of Genetics and Mutagenesis, National Institute of Health Sciences, Tokyo, Japan.
Mutat Res. 1995 Jun;329(1):1-9. doi: 10.1016/0027-5107(95)00027-g.
The expression of umuDC operon is required for UV and most chemical mutagenesis in Escherichia coli. The closely related species Salmonella typhimurium has two sets of umuDC-like operons, i.e., umuDCST in the chromosome and samAB in a 60-megadalton cryptic plasmid. In this study, we specifically disrupted the samAB genes to investigate their exact roles in UV mutagenesis in S. typhimurium. The specific gene disruption was carried out by the preligation method. Deletion of samAB did not lower the UV mutability of S. typhimurium TA2659 but rather increased the UV mutability about twofold. The samAB-umuDCST double deletion mutant as well as the umuDCST deletion mutant was UV nonmutable. These results suggest that the samAB genes do not considerably contribute to the UV mutability of S. typhimurium and raise the question of why such quiet umuDC-like genes are present in the cryptic plasmid of S. typhimurium.
在大肠杆菌中，umuDC操纵子的表达是紫外线及大多数化学诱变所必需的。密切相关的鼠伤寒沙门氏菌有两组类似umuDC的操纵子，即染色体上的umuDCST和一个60兆道尔顿隐蔽质粒中的samAB。在本研究中，我们特意破坏了samAB基因，以研究它们在鼠伤寒沙门氏菌紫外线诱变中的确切作用。通过预连接法进行特定基因破坏。缺失samAB并未降低鼠伤寒沙门氏菌TA2659的紫外线诱变率，反而使其紫外线诱变率提高了约两倍。samAB-umuDCST双缺失突变体以及umuDCST缺失突变体对紫外线均无诱变反应。这些结果表明，samAB基因对鼠伤寒沙门氏菌的紫外线诱变作用不大，并引发了一个问题，即为什么在鼠伤寒沙门氏菌的隐蔽质粒中会存在这种沉默的类似umuDC的基因。
