The leuO Gene Product Has a Latent Ability To Relieve bgl Silencing in Escherichia coli

Abstract

ABSTRACT The Escherichia coli bgl operon is of interest, since its expression is silent (phenotypically Bgl − ), at least under standard laboratory conditions. Here we attempted to identify a trans -acting factor(s) that is presumably relevant to the regulation of bgl by a random insertion mutagenesis with mini-Tn 10 . These collected mutations, conferring the phenotype of Bgl + , were localized in three loci on the genetic map, two of which appeared to be hns and bglJ , which were previously implicated as the factors affecting the Bgl phenotype. The other locus at 1 to 2 min on the genetic map appeared to be a new one. In this case, the insertion mutation was found to be just in front of the leuO gene encoding a putative LysR-like DNA-binding protein. Genetic analyses revealed that overproduction of LeuO in the wild-type cells causes the phenotype of Bgl + . A leuO deletion mutant was also characterized in terms of expression of bgl . From these results, the possible function of LeuO in bgl expression will be discussed from an evolutionary and/or ecological point of view.