title: Construction of a double hha hns mutant of Escherichia coli: effect on DNA supercoiling and alpha-haemolysin production.
abstract: A double hha hns Escherichia coli mutant was constructed. The effect of the single hns mutation and of the double hha hns mutation on the expression of the alpha-haemolysin determinant of plasmid pANN202-312 was assessed. Whereas the hns mutant moderately increased expression of the toxin, the double hha hns mutant strongly enhanced transcription of the hly operon and hence expression of the toxin. This suggests that both Hha and H-NS proteins participate in the modulation of the expression of the toxin. The enhancement of haemolysin expression in the double mutant could not be correlated to a global alteration of DNA topology: DNA preparations of a reporter plasmid isolated from this mutant gave a topoisomer distribution similar to that of the parental strain.
authors.affiliation: Departamento de Microbiología, Facultad de Biología, Universidad de Barcelona, Spain.
authors.forename: J M
authors.initials: JM
authors.lastname: Nieto
authors.forename: M
authors.initials: M
authors.lastname: Mouriño
authors.forename: C
authors.initials: C
authors.lastname: Balsalobre
authors.forename: C
authors.initials: C
authors.lastname: Madrid
authors.forename: A
authors.initials: A
authors.lastname: Prenafeta
authors.forename: F J
authors.initials: FJ
authors.lastname: Muñoa
authors.forename: A
authors.initials: A
authors.lastname: Juárez
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics*; D004269:DNA, Bacterial / Q000737:chemistry* / Q000235:genetics*; D004278:DNA, Superhelical / Q000737:chemistry* / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D006460:Hemolysin Proteins / Q000096:biosynthesis* / Q000235:genetics*; D009154:Mutation; D009690:Nucleic Acid Conformation; D010957:Plasmids / Q000737:chemistry / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004278:DNA, Superhelical; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C031908:H-NS protein, bacteria; D006460:Hemolysin Proteins; C036507:Hlya protein, E coli; C079209:hha protein, E coli