THE LEUO GENE-PRODUCT HAS A LATENT ABILITY TO RELIEVE BGL SILENCING IN ESCHERICHIA-COLI

The Escherichia coli bl operon is of interest, since its expression is silent (phenotypically Bgl(-)), at least under standard laboratory co nditions, Here we attempted to identify a trans-acting factor(s) that is presumably relevant tit the regulation of bgl by a random insertion mutagenesis with mini-Tn10. These collected mutations, conferring the phenotype of Bgl(+), were localized int three loci on the genetic map , two of which appeared to be hns and bglJ, which were previously impl icated as the factors affecting the Bgl phenotype. The other locus at 1 to 2 min on the genetic map appeared to he 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 re vealed that overproduction of LeuO in the wild-type cells causes the p henotype of Bgl(+). A lenO deletion mutant was also characterized in t erms of expression of bgl. From these results, the possible function o f LeuO in bgl expression will be discussed from an evolutionary and/or ecological point of view.