title: Rate of inversion of the Salmonella enterica shufflon regulates expression of invertible DNA.
abstract: Salmonella enterica serovar Typhi and some strains (Vi(+)) of serovar Dublin use type IVB pili to facilitate bacterial self-association, but only when the PilV proteins (potential minor pilus proteins) are not synthesized. Pilus-mediated self-association may be important in the pathogenesis of enteric fever. We have suggested that the rate of Rci-catalyzed inversion of DNA encoding the C-terminal portions of the PilV proteins controls PilV protein synthesis. This potentially represents a novel means of transcriptional control. Here, it is initially shown that DNA inversion per se is required for inhibition of gene expression from invertible DNA. Binding, without DNA scission, of Rci to its substrate sequences on DNA cannot explain the data obtained. Next, it is shown that inversion frequencies of xylE-encoding DNA, bracketed by Rci substrate sequences, may be modulated by changes in the 19-bp consensus sequences which are essential components of Rci substrate DNA. The affinity of Rci for these sequences affects inversion frequencies, so that a greater affinity is predictive of faster inversion, and therefore less synthesis of product encoded by invertible DNA. Inversion events may inhibit transcription of DNA from external promoters. In vivo, the frequency of Rci-mediated inversion is influenced by the extent of DNA supercoiling, with increasing levels of expression of invertible genes as novobiocin inhibits DNA supercoiling and thus Rci action. This inhibition of DNA supercoiling results in increased synthesis of PilV proteins as Rci activity decreases, and, in turn, bacterial self-association (particularly in serovar Dublin) decreases.
authors.affiliation: Department of Biochemistry, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China. pinecone@ust.hk
authors.forename: Connie K P
authors.initials: CK
authors.lastname: Tam
authors.forename: Jim
authors.initials: J
authors.lastname: Hackett
authors.forename: Christina
authors.initials: C
authors.lastname: Morris
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics; D007446:Chromosome Inversion; D004254:DNA Nucleotidyltransferases / Q000378:metabolism; D004269:DNA, Bacterial / Q000096:biosynthesis* / Q000378:metabolism; D004278:DNA, Superhelical / Q000037:antagonists & inhibitors / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D009675:Novobiocin / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D019779:Salmonella enterica / Q000235:genetics*; D027981:Symporters / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004278:DNA, Superhelical; D029968:Escherichia coli Proteins; C077573:PilV protein, Bacteria; D027981:Symporters; C033903:xylE protein, E coli; D009675:Novobiocin; D004254:DNA Nucleotidyltransferases; C077570:Site-specific recombinase