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 (SCCmec), an MGE that confers methicillin resistance to Staphylococcus aureus, 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 SCCmec.

中文翻译：

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由 SCCmec 元件编码的新型 DNA 引物酶-解旋酶对

移动遗传元件 (MGE) 是新酶的丰富来源，相反，了解 MGE 编码蛋白质的活性可以阐明 MGE 的功能。在这里，我们生化表征了由葡萄球菌盒式染色体 (SCCmec) 携带的保守操纵子编码的三种蛋白质，这是一种 MGE，可赋予金黄色葡萄球菌甲氧西林抗性，从而产生 MRSA 菌株。这些蛋白质中的第一个，CCPol，是一种有活性的 A 家族 DNA 聚合酶。中间蛋白 MP 与 CCPol 紧密结合并赋予它从头合成 DNA 引物的能力。CCPol-MP 复合物因此是一种独特的引物聚合酶，与任一已知引物酶家族均无关。第三种蛋白质，Cch2，是一个 3' 到 5' 的解旋酶。Cch2 还特异性结合其基因下游的 dsDNA 序列，该基因也是 CCPol-MP 引发的首选起始位点。总之，我们的结果表明这是 SCCmec 的功能复制模块。