Pettis G S, Cohen S N
Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
J Bacteriol. 2000 Aug;182(16):4500-4. doi: 10.1128/JB.182.16.4500-4504.2000.
The tra gene of Streptomyces lividans plasmid pIJ101 encodes a 621-amino-acid protein that can mediate both plasmid transfer and the interbacterial transfer of chromosomal genes (i.e., chromosome-mobilizing ability [Cma]) during mating. Here we report the results of in-frame insertional mutagenesis studies aimed at defining regions of Tra required for these functions. While hexameric linker insertions throughout the tra gene affected plasmid and chromosomal gene transfer, insertions in a 200-amino-acid region of the Tra protein that contains presumed nucleotide-binding motifs and that is widely conserved among a functionally diverse family of bacterial and plasmid proteins (K. J. Begg, S. J. Dewar, and W. D. Donachie, J. Bacteriol. 177:6211-6222, 1995) had especially prominent effects on both functions. Insertions near the N terminus of Tra reduced Cma for either circular or linear host chromosomes to a much greater extent than pIJ101 plasmid transfer. Our results suggest that Cma involves Tra functions incremental to those needed for plasmid DNA transfer.
天蓝色链霉菌质粒pIJ101的tra基因编码一种621个氨基酸的蛋白质，在接合过程中，该蛋白质既能介导质粒转移，又能介导染色体基因的细菌间转移（即染色体动员能力[Cma]）。在此，我们报告了框内插入诱变研究的结果，旨在确定这些功能所需的Tra区域。虽然tra基因中各处的六聚体接头插入都会影响质粒和染色体基因转移，但在Tra蛋白的一个200个氨基酸区域内的插入对这两种功能都有特别显著的影响，该区域包含推测的核苷酸结合基序，并且在功能多样的细菌和质粒蛋白家族中广泛保守（K. J. Begg、S. J. Dewar和W. D. Donachie，《细菌学杂志》177:6211 - 6222，1995）。Tra N端附近的插入对环状或线性宿主染色体的Cma的降低程度比对pIJ101质粒转移的降低程度大得多。我们的结果表明，Cma涉及Tra的功能，这些功能是质粒DNA转移所需功能之外增加的功能。
