1.E.54 The Gene Transfer Agent-release Holin (GTA-Hol) Family
The gene transfer agent of Rhodobacter capsulatus (RcGTA) is a bacteriophage-like genetic element with the sole known function of horizontal gene transfer. Homologues of RcGTA genes are present in many members of the alphaproteobacteria and may serve an important role in microbial gene transfer between organisms. Transcription of RcGTA genes is induced as cultures enter the stationary phase. Westbye et al. 2013 identified the promoter of the first gene in the RcGTA structural gene cluster and showed that gene transduction frequencies depend on the growth medium. Millimolar concentrations of phosphate posttranslationally inhibit the lysis-dependent release of RcGTA from cells in both a complex medium and a defined medium. Cell lysis requires the genes rcc00555 and rcc00556, which were expressed and studied in Escherichia coli to demonstrate their functions as an endolysin and holin, respectively. Production of RcGTA is regulated by host systems, including the histidine kinase, CckA, which is required for maximal expression of rcc00555 and for maturation of RcGTA to yield gene transduction-functional particles.