Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, United States.
Elife. 2020 Sep 18;9:e55478. doi: 10.7554/eLife.55478.
Mobile genetic elements (MGEs) are a rich source of new enzymes, and conversely, understanding the activities of MGE-encoded proteins can elucidate MGE function. Here, we biochemically characterize three proteins encoded by a conserved operon carried by the Staphylococcal Cassette Chromosome (SCC), an MGE that confers methicillin resistance to , creating MRSA strains. The first of these proteins, CCPol, is an active A-family DNA polymerase. The middle protein, MP, binds tightly to CCPol and confers upon it the ability to synthesize DNA primers de novo. The CCPol-MP complex is therefore a unique primase-polymerase enzyme unrelated to either known primase family. The third protein, Cch2, is a 3'-to-5' helicase. Cch2 additionally binds specifically to a dsDNA sequence downstream of its gene that is also a preferred initiation site for priming by CCPol-MP. Taken together, our results suggest that this is a functional replication module for SCC.
移动遗传元件（MGE）是新酶的丰富来源，反之，了解 MGE 编码蛋白的活性可以阐明 MGE 的功能。在这里，我们对携带于葡萄球菌盒式染色体（SCC）的保守操纵子编码的三种蛋白进行了生化特性分析，SCC 是一种赋予耐甲氧西林金黄色葡萄球菌（MRSA 菌株）的 MGE。这三种蛋白中的第一种是 CCPol，它是一种活跃的 A 家族 DNA 聚合酶。中间蛋白 MP 与 CCPol 紧密结合，并赋予其从头合成 DNA 引物的能力。因此，CCPol-MP 复合物是一种独特的引物酶 - 聚合酶酶，与已知的任何引物酶家族都没有关系。第三种蛋白 Cch2 是 3'到 5'解旋酶。Cch2 还特异性地结合到其基因下游的双链 DNA 序列，该序列也是 CCPol-MP 引发引物的首选起始位点。总的来说，我们的结果表明这是 SCC 的一个功能复制模块。
