Bacterial conjugation is an active process that results in unidirectional transfer of DNA from a donor to a recipient cell. Most transfer systems are plasmid-encoded and require proteins to act at a unique cis-acting site to initiate and complete DNA transfer. By contrast, the Mycobacterium smegmatis DNA transfer system is chromosomally encoded. Here we show that multiple cis-acting sequences present on the chromosome can mediate transfer of a non-mobilizable test plasmid. Moreover, unlike conventional plasmid transfer, recipient recombination functions are required to allow this plasmid, and derivatives of it, to re-circularize through a process similar to gap repair. Extended DNA homology with the recipient chromosome is required to facilitate repair, resulting in acquisition of recipient chromosomal DNA by the plasmid. Together, these results show that DNA transfer in M. smegmatis occurs by a mechanism different from that of prototypical plasmid transfer systems.
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We dedicate this article to the memories of S. Bardarov and J. Colston, who were friends and a stimulating intellectual force behind this work. We thank J. Colston for the recA disruption plasmids; C. Takacs, J. Flint, T. Ichiyanagi and A. Waring for technical assistance; and M. Belfort, J. Curcio, V. Derbyshire, D. Figurski, D. Nag, H. Taber and N. Tavakoli for critical comments. This work was supported by a grant from the US National Institutes of Health to K.M.D.
The authors declare no competing financial interests.
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Wang, J., Parsons, L. & Derbyshire, K. Unconventional conjugal DNA transfer in mycobacteria. Nat Genet 34, 80–84 (2003) doi:10.1038/ng1139
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