RESUMO
Strains carrying operon fusions between the promotor of the chl I gene and the lac structural genes were constructed. From these strains in which the expression of the lac genes is under the control of both nitrate and oxygen, spontaneous regulatory mutants were selected: (i) mutants which synthesize beta-galactosidase constitutively in anaerobiosis; (ii) mutants in which beta-galactosidase synthesis is no longer repressed by oxygen. Introduction of the nir R mutated allele into strains carrying these fusions resulted in the total loss of beta-galactosidase synthesis, confirming that nir R is a regulatory gene controlling the expression of the biosynthesis of the nitrate reductase.
Assuntos
Escherichia coli/genética , Regulação da Expressão Gênica , Nitrato Redutases/genética , Óperon , Anaerobiose , Bacteriófago lambda/genética , DNA Recombinante , Óperon Lac , Mutação , Oxigênio/fisiologia , beta-Galactosidase/biossínteseRESUMO
The existence of a nitrate-reductase operon in the tryptophane region was deduced from the effects of prophage insertion in each of chlI and chlC genes and from transposition of the Mu-mediated host DNA fragments of F-prime. This operon appears to be polarized from chlC to chlI and the gene order in the region is trp -- chlI -- chlC -- purB.