Identification of the rctA Gene, Which Is Required for Repression of Conjugative Transfer of Rhizobial Symbiotic Megaplasmids

• DOI: 10.1128/jb.187.21.7341-7350.2005
• Publication Date: 2005-10-19T18:57:54Z
• Authors: Daniel Pérez-Men...; Edgardo Sepúlveda; Victoria Pando; Socorro Muñoz; Joaquina Nogales; José Olivares; Maria J. Soto; José A. Herrera-...; David Romero; Susana Brom; Juan Sanjuán
• Keywords: Sinorhizobium meliloti; Transcription; Sinorhizobium; Horizontal Gene Transfer

ABSTRACT An analysis of the conjugative transfer pRetCFN42d, symbiotic plasmid (pSym) Rhizobium etli , has revealed a novel gene, rctA as an essential element regulatory system for silencing R. pSym by repressing transcription conjugal genes in standard laboratory media. The gene product lacks sequence conservation with other proteins known function but may belong to winged-helix DNA-binding subfamily transcriptional regulators. Similar that many repressors, seems be positively autoregulated. expression is greatly reduced upon overexpression another rctB previously identified putative activator transfer. Thus, counteract repressive action rctA. homologs are present at least three bacterial genomes within order Rhizobiales where they invariably located adjacent and divergently transcribed from virB -like operons. We show similar pSym, 1.35-Mb megaplasmid A Sinorhizobium meliloti also subjected inhibitory . Our data provide strong evidence S. plasmids indeed self-conjugative this property would only expressed under optimal, yet unknown conditions entail inactivation function. represent probably widespread systems controlling elements