Komano T, Yoshida T, Narahara K, Furuya N
Department of Biology, Tokyo Metropolitan University, Minamiohsawa, Hachioji-shi, Tokyo 192-0397, Japan.
Mol Microbiol. 2000 Mar;35(6):1348-59. doi: 10.1046/j.1365-2958.2000.01769.x.
The entire nucleotide sequence of the transfer region of IncI1 plasmid R64 was determined together with previously reported sequences. Twenty-two transfer genes, traE-Y and nuc, were newly identified in the present study. The protein products of 17 genes were detected by maxicell experiments or by the T7 RNA polymerase expression system. Mutagenesis experiments indicated that 16 genes were indispensable for R64 transfer both in liquid and on surfaces. In summary, the R64 transfer region located within an approximately 54 kb DNA segment was shown to encode the most complex transfer system so far studied. It contains at least 49 genes and may produce 58 different proteins as a result of shufflon DNA rearrangement and overlapping genes. Among the 49 genes, 23 tra, trb and nik genes have been shown to be indispensable for R64 conjugal transfer in liquid and on surfaces. Twelve additional pil genes are required only for liquid matings. The amino acid sequences of 10 R64 tra/trb products share similarity with those of the icm/dot products of Legionella pneumophila that are responsible for its virulence, suggesting that the R64 transfer and L. pneumophila icm/dot systems have evolved from a common ancestral genetic system.
测定了IncI1质粒R64转移区域的完整核苷酸序列，并与先前报道的序列进行了比对。本研究新鉴定出22个转移基因，即traE - Y和nuc。通过大细胞实验或T7 RNA聚合酶表达系统检测到了17个基因的蛋白质产物。诱变实验表明，16个基因对于R64在液体中和表面的转移都是必不可少的。总之，位于约54 kb DNA片段内的R64转移区域编码了迄今为止研究的最复杂的转移系统。它包含至少49个基因，由于改组基因DNA重排和重叠基因，可能产生58种不同的蛋白质。在这49个基因中，23个tra、trb和nik基因已被证明对于R64在液体中和表面的接合转移是必不可少的。另外12个菌毛基因仅在液体交配中需要。10个R64 tra/trb产物的氨基酸序列与嗜肺军团菌的icm/dot产物的氨基酸序列相似，后者与其毒力有关，这表明R64转移系统和嗜肺军团菌的icm/dot系统是从一个共同的祖先遗传系统进化而来的。
