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Functional and Mutational Analysis of Conjugative Transfer Region 2 (Tra2) from the IncHI1 Plasmid R27. Trevor D. Lawley, 2003.The transfer 2 region (Tra2) of the conjugative plasmid drR27 (derepressed R27) was analyzed by PSI-BLAST, insertional mutagenesis, genetic complementation, and an H-pilus assay . Tra2 contains 11 mating-pair formation (Mpf) genes that are essential for conjugative transfer, 9 of which are essential for H-pilus production (trhA, -L, -E, -K, -B, -V, -C, -P, and -W) . TrhK has similarity to secretin proteins, suggesting a mechanism by which DNA could traverse the outer membrane of donors . The remaining two Mpf genes, trhU and trhN, play an auxiliary role in H-pilus synthesis and are proposed to be involved in DNA transfer and mating-pair stabilization, respectively . Conjugative transfer abilities were restored for each mutant when complemented with the corresponding transfer gene . In addition to the essential Mpf genes, three genes, trhO, trhZ, and htdA, modulate R27 transfer frequency . Disruption of trhO and trhZ severely reduced the transfer frequencies of drR27, whereas disruption of htdA greatly increased the transfer frequency of wild-type R27 to drR27 levels . A comparison of the essential transfer genes encoded by the Tra2 and Tra1 (T . D . Lawley, M . W . Gilmour, J . E . Gunton, L . J . Standeven, and D . E . Taylor, J . Bacteriol . 184:2173-2183, 2002) of R27 to other transfer systems illustrates that the R27 conjugative transfer system is a chimera composed of IncF-like and IncP-like transfer systems . Furthermore, the Mpf/type IV secretion systems encoded by IncH and IncF transfer systems are distinct from that of the IncP transfer system . The phenotypic and ecological significance of these observations is discussed .
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