Differential inhibition of chromosomal genes transcription by microcin J25

NATALIA CORBALÁN; RAÚL SALOMÓN; RICARDO N. FARÍAS; PAULA A. VINCENT

Rosario, Argentina

Congreso; XLII Reunión Anual de la Sociedad Argentina de Investigaciones en Bioquímica y Biología molecular; 2006

Sociedad Argentina de Investigaciones en Bioquímica y Biología molecular

Microcin J25 (MccJ25) is an Escherichia coli antimicrobial peptide of 21 amino acids which inhibits transcription by binding to RNA polimerase (RNAP) secondary channel. The aim of the present study was to determine whether the inhibition of chromosomal genes transcription by MccJ25 is a global or a differential effect. We generated a library of transcriptional lac fusions in the chromosome of a sensitive strain (RYC1000) and b-galactosidase assays were performed to test the expression levels of these fusions in the presence and in the absence of subinhibitory concentrations of the peptide. From 100 clones studied, 96 showed a moderate repression of b-galactosidase activity (2 times), whereas in 2 clones the enzyme was strongly inhibited (24 times). Finally, 2 fusions were not affected at all by MccJ25. In one of the strains showing strong inhibition (RYC1000-17) the fusion was approximately located using a set of Hfr strains. The inactivated gene mapped somewhere between min 97 and 98 of the E. coli chromosome. Interestingly, the growth rate of RYC1000-17 was slower than that of the parental strain, suggesting that the mutated gene is involved in cellular growth. The fusion was inhibited by endogenous as well as by exogenous MccJ25. This effect was not observed in a MccJ25-resistant RNAP mutant strain indicating that the inhibition is mediated by the RNAP.