Mills D A, McKay L L, Dunny G M
Department of Microbiology and Institute for Advanced Studies in Biological Process Technology, University of Minnesota, Minneapolis 55455-0312, USA.
J Bacteriol. 1996 Jun;178(12):3531-8. doi: 10.1128/jb.178.12.3531-3538.1996.
Analysis of a region involved in the conjugative transfer of the lactococcal conjugative element pRS01 has revealed a bacteria] group II intron. Splicing of this lactococcal intron (designated Ll.ltrB) in vivo resulted in the ligation of two exon messages (ltrBE1 and ltrBE2) which encoded a putative conjugative relaxase essential for the transfer of pRS01. Like many group II introns, the Ll.ltrB intron possessed an open reading frame (ltrA) with homology to reverse transcriptases. Remarkably, sequence analysis of ltrA suggested a greater similarity to open reading frames encoded by eukaryotic mitochondrial group II introns than to those identified to date from other bacteria. Several insertional mutations within ltrA resulted in plasmids exhibiting a conjugative transfer-deficient phenotype. These results provide the first direct evidence for splicing of a prokaryotic group II intron in vivo and suggest that conjugative transfer is a mechanism for group II intron dissemination in bacteria.
对参与乳球菌接合元件pRS01接合转移的一个区域进行分析后，发现了一个细菌II类内含子。该乳球菌内含子（命名为Ll.ltrB）在体内的剪接导致两个外显子信息（ltrBE1和ltrBE2）连接，这两个外显子编码了一个对pRS01转移至关重要的假定接合松弛酶。与许多II类内含子一样，Ll.ltrB内含子拥有一个与逆转录酶具有同源性的开放阅读框（ltrA）。值得注意的是，ltrA的序列分析表明，它与真核生物线粒体II类内含子编码的开放阅读框的相似性高于迄今从其他细菌中鉴定出的开放阅读框。ltrA内的几个插入突变导致质粒表现出接合转移缺陷表型。这些结果为原核生物II类内含子在体内的剪接提供了首个直接证据，并表明接合转移是II类内含子在细菌中传播的一种机制。
