Mackenzie C, Chidambaram M, Sodergren E J, Kaplan S, Weinstock G M
Department of Biochemistry and Molecular Biology, University of Texas Medical School, Houston 77225, USA.
J Bacteriol. 1995 Jun;177(11):3027-35. doi: 10.1128/jb.177.11.3027-3035.1995.
The genome of the photosynthetic eubacterium Rhodobacter sphaeroides 2.4.1 comprises two chromosomes and five endogenous plasmids and has a 65% G+C base composition. Because of these characteristics of genome architecture, as well as the physiological advantages that allow this organism to live in sunlight when in an anaerobic environment, the sensitivity of R. sphaeroides to UV radiation was compared with that of the more extensively studied bacterium Escherichia coli. R. sphaeroides was found to be more resistant, being killed at about 60% of the rate of E. coli. To begin to analyze the basis for this increased resistance, a derivative of R. sphaeroides, strain 2.4.1 delta S, which lacks the 42-kb plasmid, was mutagenized with a derivative of Tn5, and the transposon insertion mutants were screened for increased UV sensitivity (UVs). Eight UVs strains were isolated, and the insertion sites were determined by contour-clamped homogeneous electric field pulsed-field gel electrophoresis. These mapped to at least five different locations in chromosome I. Preliminary analysis suggested that these mutants were deficient in the repair of DNA damage. This was confirmed for three loci by DNA sequence analysis, which showed the insertions to be within genes homologous to uvrA, uvrB, and uvrC, the subunits of the nuclease responsible for excising UV damage.
光合真细菌球形红杆菌2.4.1的基因组由两条染色体和五个内源质粒组成，G+C碱基组成为65%。由于这种基因组结构特点，以及该生物体在厌氧环境中能在阳光下生存的生理优势，将球形红杆菌对紫外线辐射的敏感性与研究更广泛的大肠杆菌进行了比较。结果发现球形红杆菌更具抗性，其被杀死的速率约为大肠杆菌的60%。为了开始分析这种抗性增加的基础，用Tn5的衍生物对缺乏42kb质粒的球形红杆菌衍生物2.4.1 delta S菌株进行诱变，并筛选转座子插入突变体以检测其对紫外线敏感性增加（UVs）的情况。分离出八个UVs菌株，并通过轮廓钳制均匀电场脉冲场凝胶电泳确定插入位点。这些位点定位于染色体I的至少五个不同位置。初步分析表明这些突变体在DNA损伤修复方面存在缺陷。通过DNA序列分析对三个位点进行了确认，结果显示插入发生在与uvrA、uvrB和uvrC同源的基因内，uvrA、uvrB和uvrC是负责切除紫外线损伤的核酸酶的亚基。
