02085nas a2200265   4500000000100000008004100001653001700042653001800059653002000077653002100097653002400118653001700142653001200159100001300171700001100184700001100195700001200206700001300218700001400231700001400245700001300259245011500272520141800387022001401805       2014                            d10aDNA topology10aCell Division10aElectroporation10aPartition errors10aPlasmid segregation10aTuberculosis10aleprosy1 aPanas MW1 aJain P1 aYang H1 aMitra S1 aBiswas D1 aWattam AR1 aLetvin NL1 aJacobs W00aNoncanonical SMC protein in Mycobacterium smegmatis restricts maintenance of Mycobacterium fortuitum plasmids.3 a<p>Research on tuberculosis and leprosy was revolutionized by the development of a plasmid transformation system in the fast-growing surrogate, Mycobacterium smegmatis. This transformation system was made possible by the successful isolation of a M. smegmatis mutant strain mc(2)155, whose efficient plasmid transformation (ept) phenotype supported the replication of Mycobacterium fortuitum pAL5000 plasmids. In this report, we identified the EptC gene, the loss of which confers the ept phenotype. EptC shares significant amino acid sequence homology and domain structure with the MukB protein of Escherichia coli, a structural maintenance of chromosomes (SMC) protein. Surprisingly, M. smegmatis has three paralogs of SMC proteins: EptC and MSMEG_0370 both share homology with Gram-negative bacterial MukB; and MSMEG_2423 shares homology with Gram-positive bacterial SMCs, including the single SMC protein predicted for Mycobacterium tuberculosis and Mycobacterium leprae. Purified EptC was shown to bind ssDNA and stabilize negative supercoils in plasmid DNA. Moreover, an EptC-mCherry fusion protein was constructed and shown to bind to DNA in live mycobacteria, and to prevent segregation of plasmid DNA to daughter cells. To our knowledge, this is the first report of impaired plasmid maintenance caused by a SMC homolog, which has been canonically known to assist the segregation of genetic materials.</p>  a1091-6490