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TraA, TraC and TraD autorepress two divergent quorum‐regulated promoters near the transfer origin of the Ti plasmid of Agrobacterium tumefaciens
Author(s) -
Cho Hongbaek,
Winans Stephen C.
Publication year - 2007
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2007.05624.x
Subject(s) - biology , operon , regulon , agrobacterium tumefaciens , plasmid , ti plasmid , genetics , promoter , gene , trac , regulation of gene expression , transgene , gene expression , escherichia coli , computer science , programming language
Summary Whole‐genome transcriptional profiling experiments were performed to identify the complete set of TraR‐regulated genes in isogenic A. tumefaciens strains containing an octopine‐type or nopaline‐type Ti plasmid. Most of the known TraR‐regulated genes as well as a number of new inducible genes were identified. Surprisingly, some known members of this regulon showed both weaker induction and weak levels of expression than we had predicted based upon earlier studies. In particular, traA was expressed at surprisingly weak levels. Genetic analysis showed that the traAFBH operon is repressed by formation of a putative relaxosome at oriT consisting the TraA, TraC and TraD. These proteins also repressed the divergent traCDGyci operon. TraA was essential for oriT processing, and both TraC and TraD were necessary for the efficient processing, although some processing occurred in their absence. Likewise, Ti plasmid conjugation required TraA, TraF and TraG, and occurred at reduced levels in the absence of TraC or TraD. TraA preferentially acted in cis in repressing the traA and traC promoters and in the processing of oriT , which explains the very high activity of plasmid‐borne traA–lacZ fusions reported in previous studies.