Identification of PhoP-PhoQ activated genes within a duplicated region of theSalmonella typhimuriumchromosome

Abstract

Salmonellae virulence requires the PhoP-PhoQ two-component regulatory system. PhoP-PhoQ activate the transcription of genes following phagocytosis by macrophages which are necessary for survival within the phagosome environment. Thirteen previously undefined PhoP-activated gene fusions generated by MudJ and TnphoA(pag A, andE-P, respectively) were cloned and sequenced. Mostpagproducts show no similarity to proteins in the database, while others are predicted to encode: a UDP-glucose dehydrogenase (pagA); a protein with similarity to the product of anE. colialuminium-induced gene (pagH); a protein encoded within aSalmonella-unique region adjacent to thesinRgene (pagN); a protein similar to a product of theYersiniavirulence plasmid (pagO); and a protein with similarity to CrcA which is necessary for resistance ofE. colito camphor (pagP). Of thepagcharacterized, onlypagK, MandOwere closely linked.pagJandpagKwere shown to be unlinked but nearly identical in DNA sequence, as each was located within a 1.6 kb DNA duplication. The translations of sequences surroundingpagJandpagKshow similarity to proteins from extrachromosomal elements as well as those involved in DNA transposition and rearrangement, suggesting that this region may have been or is a mobile element. The transcriptional start sites ofpagK, M, andJwere determined; however, comparison to other knownpaggene promoters failed to reveal a consensus sequence for PhoP-regulated activation. DNA sequences hybridizing to aSalmonella typhimurium pagKspecific probe were found inS. enteritidisbut absent in otherSalmonellaserotypes and Enterobacteriaceae tested, suggesting that these genes are specific for broad host range Salmonellae that cause diarrhoea in humans. Cumulatively, these data further demonstrate: (1) that PhoP-PhoQ is a global regulator of the production of diverse envelope or secreted proteins; (2) that PhoP-PhoQ regulate the production of proteins of redundant function; and (3) thatpagare often located in regions of horizontally acquired DNA that are absent in other Enterobacteriaceae.