Zhao Junhua, Lambowitz Alan M
Institute for Cellular and Molecular Biology, Department of Chemistry and Biochemistry, and Section of Molecular Genetics and Microbiology, University of Texas, Austin, TX 78712, USA.
Proc Natl Acad Sci U S A. 2005 Nov 8;102(45):16133-40. doi: 10.1073/pnas.0507057102. Epub 2005 Sep 26.
The Lactococcus lactis Ll.LtrB group II intron encodes a reverse transcriptase (LtrA protein) that binds the intron RNA to promote RNA splicing and intron mobility. Here, we used LtrA-GFP fusions and immunofluorescence microscopy to show that LtrA localizes to cellular poles in Escherichia coli and Lactococcus lactis. This polar localization occurs with or without coexpression of Ll.LtrB intron RNA, is observed over a wide range of cellular growth rates and expression levels, and is independent of replication origin function. The same localization pattern was found for three nonoverlapping LtrA subsegments, possibly reflecting dependence on common redundant signals and/or protein physical properties. When coexpressed in E. coli, LtrA interferes with the polar localization of the Shigella IcsA protein, which mediates polarized actin tail assembly, suggesting competition for a common localization determinant. The polar localization of LtrA could account for the preferential insertion of the Ll.LtrB intron in the origin and terminus regions of the E. coli chromosome, may facilitate access to exposed DNA in these regions, and could potentially link group II intron mobility to the host DNA replication and/or cell division machinery.
乳酸乳球菌Ll.LtrB II类内含子编码一种逆转录酶（LtrA蛋白），该蛋白结合内含子RNA以促进RNA剪接和内含子移动。在此，我们使用LtrA-GFP融合蛋白和免疫荧光显微镜技术来表明LtrA定位于大肠杆菌和乳酸乳球菌的细胞两极。无论是否共表达Ll.LtrB内含子RNA，这种极性定位都会出现，在广泛的细胞生长速率和表达水平范围内都能观察到，并且与复制起点功能无关。对于三个不重叠的LtrA亚片段也发现了相同的定位模式，这可能反映了对共同冗余信号和/或蛋白质物理特性的依赖性。当在大肠杆菌中共表达时，LtrA会干扰志贺氏菌IcsA蛋白的极性定位，IcsA蛋白介导极化肌动蛋白尾的组装，这表明存在对共同定位决定因素的竞争。LtrA的极性定位可能解释了Ll.LtrB内含子在大肠杆菌染色体的起点和终点区域的优先插入，可能有助于接触这些区域中暴露的DNA，并可能将II类内含子的移动性与宿主DNA复制和/或细胞分裂机制联系起来。
