Inamoto S, Yoshioka Y, Ohtsubo E
Institute of Applied Microbiology, University of Tokyo, Japan.
J Bacteriol. 1988 Jun;170(6):2749-57. doi: 10.1128/jb.170.6.2749-2757.1988.
The nucleotide sequence of part of the tra region of R100 including traJ and traY was determined, and the products of several tra genes were identified. The nucleotide sequence of traJ, encoding a protein of 223 amino acids, showed poor homology with the corresponding segments of other plasmids related to R100, but the deduced amino acid sequences showed low but significant homology. The first four amino acids at the N-terminal region of the TraJ protein were not essential for positive regulation of expression of traY, the first gene of the traYZ operon. The nucleotide sequence of traY shows that this gene may use TTG as the initiation codon and that it encodes a protein of 75 amino acids. Analysis of the traY gene product, which was obtained as the fusion protein with beta-galactosidase, showed that the N-terminal region of the product has an amino acid sequence identical to that deduced from the assigned frame but lacks formylmethionine. traY of plasmid F, which encodes a larger protein than the TraY protein of R100, is thought to use ATG as an initiation codon. However, a TTG initiation codon was found in the preceding region of the previously assigned traY coding frame of F. Interestingly, when translation of traY of F was initiated from TTG, the amino acid sequence homologous to the TraY protein of R100 appeared in tandem in the TraY protein of F. This may suggest that traY of F has undergone duplication of a gene like the traY gene of R100.
测定了R100的tra区域中包括traJ和traY在内的部分核苷酸序列，并鉴定了几个tra基因的产物。编码含223个氨基酸的蛋白质的traJ核苷酸序列，与其他与R100相关质粒的相应片段同源性较差，但推导的氨基酸序列显示出低但显著的同源性。TraJ蛋白N端区域的前四个氨基酸对于traYZ操纵子的第一个基因traY表达的正调控不是必需的。traY的核苷酸序列表明，该基因可能使用TTG作为起始密码子，并且它编码一个含75个氨基酸的蛋白质。对作为与β-半乳糖苷酶融合蛋白获得的traY基因产物的分析表明，该产物的N端区域具有与从指定阅读框推导的氨基酸序列相同，但缺少甲酰甲硫氨酸。质粒F的traY编码的蛋白质比R100的TraY蛋白大，被认为使用ATG作为起始密码子。然而，在先前指定的F的traY编码框的前面区域发现了一个TTG起始密码子。有趣的是，当F的traY从TTG开始翻译时，与R100的TraY蛋白同源的氨基酸序列在F的TraY蛋白中串联出现。这可能表明F的traY像R100的traY基因一样经历了基因重复。
