Transfer functions of the Streptococcus faecalis plasmid pAD1: organization of plasmid DNA encoding response to sex pheromone

Abstract

The conjugative plasmid pAD1 (59.6 kilobases) of Streptococcus faecalis shows a 10,000-fold increase in transfer frequency following induction by the sex pheromone cAD1. Mutagenesis of the plasmid with transposon Tn917 was undertaken to determine the region(s) of pAD1 required for the mating response. The relevant genetic material was found to be distributed over a 31.2-kilobase contiguous region of the plasmid. Although insertions in two previously identified regions (traA and traB) exhibited increased transfer frequencies, insertions in five new regions (D, E, F, G, and H) decreased the ability of pAD1 to transfer. Insertions in region H allowed the cells to form visible mating aggregates, but the plasmid transfer frequency was decreased to levels below detection during a 1-h broth mating. Mutants with mutations in region G were able to form aggregates; however, insertions in regions D, E, and F prevented aggregate formation. Insertions in region C decreased the sensitivity of the cell to exogenous cAD1 and exhibited increased activity of the pheromone inhibitor iAD1. Surface protein profiles produced by a number of these mutants were examined, and in some cases were found to be different from those of the wild type. A map showing the various regions is presented, and related aspects of the regulation of the pAD1 mating response are discussed.