Regulation of plasmid gene expression and transfer by TraM

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This plasmid encoded DNA binding protein is essential for conjugation. Part of its function is transcriptional as it regulates its own expression, although we have shown that its most critical function is to recruit the plasmid to the conjugative pore for transfer. Our work has shown that TraM is a two domain protein consisting of an N-terminal RHH DNA reading head and a C-terminal oligomerization domain. The C-terminal domain specifically binds the C-terminal tail of the coupling protein, TraD, which forms the cytoplasmic face of the conjugative pore. This interaction is essential for transfer of the plasmid to the pore and also ensures that only the correct, cognate plasmid is transferred. TraM cooperatively binds DNA as an intriguing dimer of tetramers. There are no protein-protein contacts between the tetramers on the DNA, instead, we demonstrated that cooperativity involves TraM-induced DNA unwinding and kinking. We also showed that A. tumefaciens VirC2, a functional homologue of F plasmid TraM, forms a highly novel, single chain RHH fold to regulate T-DNA transfer from A. tumefaciens to various plants.

Figure 1.
Wong, J. J., Lu, J., Edwards, R. A., Frost, L. S., Glover, J. N. M. (2011) Structural basis of cooperative DNA recognition by the plasmid conjugation factor, TraM. Nucleic Acids Research Epub ahead of print
Lu, J., den Dulk-Ras, A., Hooykaas, P. J. and Glover, J. N. M. (2009) Agrobacterium tumefaciens VirC2 enhances T-DNA transfer and virulence through its C-terminal ribbon-helix-helix DNA-binding fold. PNAS 106(24):9643-9648. PDF
Lu, J., Wong, J. J. W., Edwards, R. A., Manchak, J., Frost, L. S. and Glover, J. N. M. (2008) Structural basis of specific TraD-TraM recognition during F plasmid-mediated bacterial conjugation. Molecular Microbiology 70(1):89-99. PDF
Lu, J., Edwards, R. A., Wong, J. J. W., Manchak, J. Scott, P. G., Frost, L. S. and Glover, J. N. M. (2006) Protonation-mediated structural flexibility in the F conjugation regulatory protein, TraM. EMBO Journal 25(12):2930-2939. PDF