Fomenko Dmitri E, Metlitskaya Anastazia Z, Péduzzi Jean, Goulard Christophe, Katrukha Genrikh S, Gening Leonid V, Rebuffat Sylvie, Khmel Inessa A
Institute of Molecular Genetics, Russian Academy of Sciences, Moscow, Russia.
Antimicrob Agents Chemother. 2003 Sep;47(9):2868-74. doi: 10.1128/AAC.47.9.2868-2874.2003.
Microcin C51 (MccC51) is an antimicrobial nucleotide-heptapeptide produced by a natural Escherichia coli strain. A 5.7-kb fragment of the pC51 plasmid carrying the genes involved in MccC51 production, secretion, and self-immunity was sequenced, and the genes were characterized. The sequence of the MccC51 gene cluster is highly similar to that of the MccC7 gene. Recombinant plasmids carrying different combinations of the mcc genes involved in the MccC51 production or immunity were constructed to characterize their functional roles. The mccA, mccB, mccD, and mccE genes are involved in MccC51 production, while the mccC and mccE genes are responsible for immunity to MccC51. The mcc gene cluster is flanked by 44-bp direct repeats. Amino acid sequence comparisons allowed us to propose functions for each Mcc polypeptide in MccC51 biosynthesis. Plasmid pUHN containing the cloned mccA, mccB, mccC, and mccE genes, but lacking mccD, directed the synthesis of MccC51p, a substance chemically related to MccC51. MccC51p exhibited weak antibiotic activity against E. coli and was toxic to the producing cells. The immunity to exogenous MccC51 determined by the mccC and mccE genes did not overcome the toxic action of MccC51p on the producing cells. The G+C content of the MccC51 operon, markedly lower than that of the E. coli genome, and the presence of direct repeats suggest the possibility of horizontal transfer of this gene cluster.
微菌素C51（MccC51）是一种由天然大肠杆菌菌株产生的抗菌核苷酸七肽。对携带参与MccC51产生、分泌和自身免疫相关基因的pC51质粒的一个5.7 kb片段进行了测序，并对这些基因进行了表征。MccC51基因簇的序列与MccC7基因的序列高度相似。构建了携带参与MccC51产生或免疫的mcc基因不同组合的重组质粒，以表征它们的功能作用。mccA、mccB、mccD和mccE基因参与MccC51的产生，而mccC和mccE基因负责对MccC51的免疫。mcc基因簇两侧是44 bp的直接重复序列。氨基酸序列比较使我们能够推测出每个Mcc多肽在MccC51生物合成中的功能。含有克隆的mccA、mccB、mccC和mccE基因但缺少mccD的质粒pUHN指导了与MccC51化学相关的物质MccC51p的合成。MccC51p对大肠杆菌表现出微弱的抗生素活性，并且对产生细胞有毒性。由mccC和mccE基因决定的对外源MccC51的免疫并不能克服MccC51p对产生细胞的毒性作用。MccC51操纵子的G+C含量明显低于大肠杆菌基因组，并且存在直接重复序列，这表明该基因簇可能存在水平转移。
