Pheromone-Regulated Expression of Sex Pheromone Plasmid pAD1-Encoded Aggregation Substance Depends on at Least Six Upstream Genes and a cis -Acting, Orientation-Dependent Factor

Open Access
Publisher Website
Google Scholar
Abstract
Conjugative transfer of Enterococcus faecalis -specific sex pheromone plasmids relies on an adhesin, called aggregation substance, to confer a tight cell-to-cell contact between the mating partners. To analyze the dependence of pAD1-encoded aggregation substance, Asa1, on pheromone induction, a variety of upstream fragments were fused to an α-amylase reporter gene, amyL , by use of a novel promoter probe vector, pAMY-em1. For pheromone-regulated α-amylase activity, a total of at least six genes, traB , traC , traA , traE1 , orfY , and orf1 , are required: TraB efficiently represses asa1 (by a mechanism unrelated to its presumptive function in pheromone shutdown, since a complete shutdown is observed exclusively in the presence of traC ); only traC can relieve traB -mediated repression in a pheromone-dependent manner. In addition to traB , traA is required but not sufficient for negative control. Mutational inactivation of traE1 , orfY , or orf1 , respectively, results in a total loss of α-amylase activity for constructs normally mediating constitutive expression. Inversion of a fragment covering traA , P 0 , and traE1 without disrupting any gene or control element switches off amyL or asa1 expression, indicating the involvement of a cis -acting, orientation-dependent factor (as had been shown for plasmid pCF10). Unexpectedly, pAD1 represses all pAMY-em1 derivatives in trans , while its own pheromone-dependent functions are unaffected. The discrepancy between the new data and those of former studies defining TraE1 as a trans -acting positive regulator is discussed.

This publication has 33 references indexed in Scilit: