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The expression of a novel antisense gene mediates incompatibility within the large repABC family of α‐proteobacterial plasmids
Author(s) -
MacLellan Shawn R.,
Smallbone Laura A.,
Sibley Christopher D.,
Finan Turlough M.
Publication year - 2005
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.1365-2958.2004.04412.x
Subject(s) - biology , replicon , genetics , gene , plasmid , sinorhizobium meliloti , extrachromosomal dna , untranslated region , intergenic region , genome , rna , mutant
Summary Large extrachromosomal replicons in many members of the α‐proteobacteria encode genes that are required for plant or animal pathogenesis or symbiosis. Most of these replicons encode repABC genes that control their replication and faithful segregation during cell division. In addition to its chromosome, the plant endosymbiont Sinorhizobium meliloti also maintains the 1.4 Mb pSymA and 1.7 Mb pSymB symbiotic megaplasmids both of which are repABC ‐type replicons. In all repABC loci that have been characterized, an apparently untranslated intergenic region between the repB and repC genes encodes a strong incompatibility determinant (referred to as incα). Here we report the isolation of mutations within the incα regions of pSymA and pSymB that eliminate incompatibility. These mutations map to and inactivate a promoter in the intergenic region that drives the expression of an approximately 56 nucleotide untranslated RNA molecule that mediates incompatibility. This gene, that we have named incA , is transcribed antisense to the repABC genes. Our analysis suggests that the incA gene is conserved in repABC loci from a diverse spectrum of bacteria.