TraM of plasmid R1 controls transfer gene expression as an integrated control element in a complex regulatory network

Abstract

SummarySite-directed mutagenesis was used to investigate the functions of the traM gene in plasmid R1-mediated bacterial conjugation. Three mutant alleles, a null mutation, a sense mutation and a stop mutation, were recombined back into the R1-16 plasmid, a transferderepressed (finO ¹ ) variant of plasmid R1. The frequency of conjugative transfer of the traM null mutant derivative of R1-16 was 10 7 -fold lower than that of the isogenic parent plasmid, showing the absolute requirement for this gene in conjugative transfer of plasmid R1. Measurements of the abundance of plasmid specified traJ, traA and traM mRNAs, TraM protein levels, and complementation studies indicated that the traM gene of plasmid R1 has at least two functions in conjugation: (i) positive control of transfer gene expression; and (ii) a function in a process distinct from gene expression. Since expression of the negatively autoregulated traM gene is itself affected positively by the expression of the transfer operon genes, this gene constitutes a decisive element within a regulatory circuit that co-ordinates expression of the genes necessary for horizontal DNA transfer. Based on our studies, we present a novel model for the regulation of the transfer genes of plasmid R1 that might also be applicable to other IncF plasmids.

Conjugative coupling proteins interact with cognate and heterologous VirB10-like proteins while exhibiting specificity for cognate relaxosomes

“…In the case of the related F-like conjugative plasmids, the roles of TrwA seem to be performed by the conjunction of the oriT-binding proteins TraY and TraM, which are functionally redundant to some extent (44). Both proteins, like R388 TrwA, are involved in transcriptional regulation of transfer genes and in activating the relaxase nicking activity (29,(45)(46)(47). Protein TraY is homologous only to the N-terminal DNA-binding domain of TrwA.…”

Transfer Protein TraY of Plasmid R1 Stimulates TraI-Catalyzed oriT Cleavage In Vivo

“…Interestingly, although the cleavage assays demonstrate that TraM and TraY independently promote strand scission in vivo, TraM remained essential for mobilization of the R1 origin even in the presence of TraY. These findings suggest that, whereas TraY and TraM function may overlap to a certain extent in the R1 relaxosome, TraM additionally performs a second function that is essential for successful conjugative transmission of plasmid DNA.The traM and traY genes of IncF conjugation systems are essential for transfer proficiency (19,24,25,35). Numerous studies have established a role for traM and traY in regulation of transfer gene expression (6,7,34,35,41).…”

“…The traM and traY genes of IncF conjugation systems are essential for transfer proficiency (19,24,25,35). Numerous studies have established a role for traM and traY in regulation of transfer gene expression (6,7,34,35,41).…”

What traits are carried on mobile genetic elements, and why?

“…For example, there is a large variance in the transmissibility of bacterial plasmids (Dionisio et al, 2002), and selection is likely to exert an effect upon hosts to reduce the amount of conjugation if transfer is costly. Thus, in many plasmids the expression of the conjugation machinery depends on cell density (Kozlowicz et al, 2006), or is repressed after some lag upon acquisition of the plasmid (Polzleitner et al, 1997), presumably because by then most recipients cells already contain the plasmid and the costs of conjugation offset the gains in transfer.…”