The gene transfer agent of Rhodobacter capsulatus and "constitutive transduction" in prokaryotes

Transduction, bacteriophage-mediated gene transfer, is thought to play an i mportant role in the evolution of prokaryote genomes. Several gene transfer agents that resemble transducing phages have been found in diverse prokary otes. This mini-review discusses these interesting agents of genetic exchan ge with a focus on the gene transfer agent (GTA) of Rhodobacter capsulatus, at present the only member of this group for which genetic information exi sts about the production of transducing particles. Production of GTA result s from expression of genes that are similar to phage genes, yet transcripti on of these genes is dependent upon cellular (two-component) signaling prot eins. The significance of these relationships, as well as the finding of GT A gene homologues in the bacterium Rhodopseudomonas palustris, is discussed .