THE RAP AND HOR PROTEINS OF ERWINIA, SERRATIA AND YERSINIA - A NOVEL SUBGROUP IN A GROWING SUPERFAMILY OF PROTEINS REGULATING DIVERSE PHYSIOLOGICAL PROCESSES IN BACTERIAL PATHOGENS

The enteric bacterium Serratia marcescens is an opportunistic human pa thogen. The strain ATCC39006 makes the red pigment, prodigiosin (Pig), and the beta-lactam antibiotic carbapenem (Car), Mutants were isolate d that were concomitantly defective for Pig and Car production. These mutants were found to have a mutation in the rap gene (regulation of a ntibiotic and pigment). Sequence analysis of the rap gene revealed a p redicted protein product showing strong homology to SlyA, originally t hought to be a haemolytic Virulence determinant in Salmonella typhimur ium. Homologues of rap were detected in several bacterial genera, incl uding Salmonella, Yersinia, Enterobacter, and species of the plant pat hogen, Erwinia. The Erwinia hor(Er) (homologue of rap) and the Yersini a hor(Ye), genes were also found to be very similar to rap and slyA. M arker exchange mutagenesis of hor(Er) revealed that it encoded a regul atory protein controlling the production of antibiotic and exoenzyme V irulence determinants in the phytopathogen, Erwinia carotovora subspec ies carotovora. We have shown that these new homologues of SlyA form a highly conserved subgroup of a growing superfamily of bacterial regul atory proteins controlling diverse physiological processes in human, a nimal and plant pathogens.