期刊
JOURNAL OF BACTERIOLOGY
卷 188, 期 17, 页码 6346-6353出版社
AMER SOC MICROBIOLOGY
DOI: 10.1128/JB.00462-06
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- Austrian Science Fund FWF [P 18607] Funding Source: Medline
- NHLBI NIH HHS [T35 HL007763, 5T35 HL07763] Funding Source: Medline
- NIGMS NIH HHS [T32 GM07270, T32 GM007270] Funding Source: Medline
- NATIONAL HEART, LUNG, AND BLOOD INSTITUTE [T35HL007763] Funding Source: NIH RePORTER
- NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES [T32GM007270] Funding Source: NIH RePORTER
Bacteria commonly exchange genetic information by the horizontal transfer of conjugative plasmids. In gram-negative conjugation, a relaxase enzyme is absolutely required to prepare plasmid DNA for transit into the recipient via a type IV secretion system. Here we report a mutagenesis of the F plasmid relaxase gene traI using in-frame, 31-codon insertions. Phenotypic analysis of our mutant library revealed that several mutant proteins are functional in conjugation, highlighting regions of TraI that can tolerate insertions of a moderate size. We also demonstrate that wild-type TraI, when overexpressed, plays a dominant-negative regulatory role in conjugation, repressing plasmid transfer frequencies similar to 100-fold. Mutant TraI proteins with insertions in a region of approximately 400 residues between the consensus relaxase and helicase sequences did not cause conjugative repression. These unrestrictive TraI variants have normal relaxase activity in vivo, and several have wild-type conjugative functions when expressed at normal levels. We postulate that TraI negatively regulates conjugation by interacting with and sequestering some component of the conjugative apparatus. Our data indicate that the domain responsible for conjugative repression resides in the central region of TraI between the protein's catalytic domains.
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