Noncanonical SMC protein in Mycobacterium smegmatis restricts maintenance of Mycobacterium fortuitum plasmids

Michael W. Panas, Paras Jain, Hui Yang, Shimontini Mitra, Debasis Biswas, Alice Rebecca Wattam, Norman L. Letvin, William R. Jacobs

Research output: Contribution to journalArticlepeer-review

39 Scopus citations


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 mc2155, 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 Gramnegative 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.

Original languageEnglish (US)
Pages (from-to)13264-13271
Number of pages8
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number37
StatePublished - 2014


  • Cell division
  • DNA topology
  • Electroporation
  • Partition errors
  • Plasmid segregation

ASJC Scopus subject areas

  • General


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