Olschläger T, Braun V
Mikrobiologie II, Universität Tübingen, Federal Republic of Germany.
J Bacteriol. 1987 Oct;169(10):4765-9. doi: 10.1128/jb.169.10.4765-4769.1987.
Escherichia coli strains carrying the cmi locus on plasmids are immune against colicin M, which primarily inhibits murein biosynthesis, followed by lysis of cells. The nucleotide sequence of the cmi region was determined. It contains an open reading frame for a polypeptide with a molecular weight of 19,227. However, the major protein band observed on polyacrylamide gels after transcription and translation in an in vitro system or in minicells had an apparent molecular weight between 15,000 and 16,000. The nucleotide sequence contained internal ATG codons, two of which could serve for the synthesis of polypeptides with molecular weights of 15,349 and 15,996, respectively. A subclone with a DNA fragment that encoded these two shorter polypeptides exhibited full immunity. The colicin M immunity protein was found in the cytoplasmic membrane. The colicin M activity and immunity genes were transcribed in opposite directions. Both properties are typical of the channel-forming colicins and are in contrast to the colicins with endonuclease activities. However, colicin M does not form channels and exhibits no structural similarity to channel-forming colicins.
携带位于质粒上的cmi位点的大肠杆菌菌株对大肠菌素M具有免疫性，大肠菌素M主要抑制胞壁质生物合成，随后导致细胞裂解。测定了cmi区域的核苷酸序列。它包含一个分子量为19227的多肽的开放阅读框。然而，在体外系统或小细胞中转录和翻译后，聚丙烯酰胺凝胶上观察到的主要蛋白带的表观分子量在15000至16000之间。核苷酸序列包含内部ATG密码子，其中两个分别可用于合成分子量为15349和15996的多肽。一个携带编码这两种较短多肽的DNA片段的亚克隆表现出完全免疫性。大肠菌素M免疫蛋白存在于细胞质膜中。大肠菌素M活性基因和免疫基因以相反方向转录。这两种特性是形成通道的大肠菌素的典型特征，与具有核酸内切酶活性的大肠菌素相反。然而，大肠菌素M不形成通道，并且与形成通道的大肠菌素没有结构相似性。
