IDENTIFICATION OF PHOP-PHOQ ACTIVATED GENES WITHIN A DUPLICATED REGION OF THE SALMONELLA-TYPHIMURIUM CHROMOSOME

Salmonellae virulence requires the PhoP-PhoQ two-component regulatory system. PhoP-PhoQ activate the transcription of genes following phagoc ytosis by macrophages which are necessary for survival within the phag osome environment. Thirteen previously undefined PhoP-activated gene f usions generated by MudJ and TnphoA (pag A, and E-P, respectively) wer e cloned and sequenced. Mostpag products show no similarity to protein s in the database, while others are predicted to encode: a UDP-glucose dehydrogenase (pagA); a protein with similarity to the product of an E. coli aluminium-induced gene (pagH); a protein encoded within a Salm onella-unique region adjacent to the sinR gene (pagN); a protein simil ar to a product of the Yersinia virulence plasmid (pagO); and a protei n with similarity to CrcA which is necessary for resistance of E. coli to camphor (pagP). Of the pag characterized, only pagK, M and O were closely linked. pagJ and pagK were shown to be unlinked but nearly ide ntical in DNA sequence, as each was located within a 1.6 kb DNA duplic ation. The translations of sequences surrounding pagJ and pagK show si milarity to proteins from extrachromosomal elements as well as those i nvolved in DNA transposition and rearrangement, suggesting that this r egion may have been or is a mobile element. The transcriptional start sites of pagK, M, and J were determined; however, comparison to other known pag gene promoters failed to reveal a consensus sequence for Pho P-regulated activation. DNA sequences hybridizing to a Salmonella typh imurium pagK specific probe were found in S. enteritidis but absent in other Salmonella serotypes and Enterobacteriaceae tested, suggesting that these genes are specific for broad host range Salmonellae that ca use 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 produc tion of proteins of redundant function; and (3) that pag are often loc ated in regions of horizontally acquired DNA that are absent in other Enterobacteriaceae. (C) 1998 Academic Press.