Functional analysis of bacterial reverse transcriptase genes and retroelements in pathogenic bacteria

细菌逆转录酶负责合成卫星RNA-DNA复合体，称为多拷贝单链DNA(MsDNA)。MsDNA合成所需的一个遗传元件称为反转录病毒启动子，它由msr-msd区、msDNA编码区和ret基因组成，ret基因是逆转录酶的编码区。虽然反转录和msDNA的作用尚不清楚(S)，但已有报道称，在大肠杆菌中，在msDNA过度生产的情况下，突变频率会增加。到目前为止，我们已经证明了msDNA在霍乱弧菌、副溶血性弧菌等病原菌中的存在，并从它们的染色体上克隆了反转录基因区域。最近发现msDNA和/或逆转录酶与细菌致病性之间的关系。本研究的主要目的是探讨霍乱弧菌msDNA和/或逆转录酶与致病性的关系。研究发现，霍乱毒素基因(CtxAB)、肠道定植因子基因(TcpA)、ompU等毒力基因在ret突变体中高度表达，提示msDNA和/或逆转转移酶参与了霍乱弧菌毒力基因的调控。结果表明，Retron-St85的G+C含量和密码子使用与鼠伤寒沙门氏菌基因组的G+C含量和密码子使用有显著差异，表明该细菌可能是最近才获得的retron-St85。

Bacterial reverse transcriptase is responsible for the synthesis of satellite RNA-DNA complex called multicopy single-stranded DNA(msDNA). A genetic element required for the msDNA synthesis is named retron which consists of the msr-msd region, a coding region for the msDNA and the ret gene, a coding region for reverse transcriptase. Although the role(s) of retron and msDNA remains unclear, it has been reported that mutation frequency was increased in Escherichia coli under conditions in which msDNA was overproduced in a cell.To date, we have demonstrated the existence of msDNA in pathogenic bacteria, such as Vibrio cholerae, V.parahaemolyticus, and so on, and cloned the retron regions from their chromosomes. A relationship between msDNA and/or reverse transcriptase and bacterial pathogenicity has been suggested recently. A major purpose of this study is to investigate the relationship between msDNA and/or reverse transcriptase and pathogenicity in pathogenic bacteria.In this study, differential gene expression between wild-type V.cholerae and a ret gene mutant was examined by microarray analysis. It was found that virulence genes, such as the cholera toxin genes (ctxAB), the intestinal colonization factor gene (tcpA), ompU, and so on, were highly expressed in the ret mutant, suggesting that the msDNA and/or reverse transciptase is involved in regulation of those virulence genes in V.cholerae.A novel msDNA, msDNA-St85, from Salmonella enterica serovar Typhimurium was isolated and characterized. It was found that the G+C content and the codon usage of retron-St85 were significantly different from those of the S.Typhimurium genome, indicating that retron-St85 was probably acquired recently in this bacterium.