The leucine regulon of Escherichia coli K-12: a mutation in rblA alters expression of L-leucine-dependent metabolic operons

Abstract

We have isolated and characterized a highly pleiotropic Escherichia coli mutant affected in the activity of a number of enzymes involved in different metabolic pathways, all of which are regulated by leucine. Selected for its ability to grow with L-serine as sole carbon source, the rbl-1::TnlO mutant had high levels of L-serine deaminase activity (due to increased transcription of the structural gene) and of another amino acid-degrading enzyme, L-threonine dehydrogenase, and decreased transcription of the operons serA and UvIH, coding for biosynthetic enzymes. The rbl mutation suppressed the slow growth of a metK mutant, deficient in S-adenosylmethionine synthetase. Furthermore, metK mutants spontaneously accumulated faster-growing rbl-like derivatives, and a commonly used metK strain, RG62, carries such a mutation. The rbl gene is located near 20 min on the E. coli genetic map. All phenotypes of the rbl mutant could be observed in rbl+ strains cultivated in the presence of L-leucine, and exogenous L-leucine had little further effect on the rbl strains. We propose that the rbl gene product is the regulator of a global response to leucine.

The tdh and serA operons of Escherichia coli: mutational analysis of the regulatory elements of leucine-responsive genes

“…,B-Galactosidase assays on these strains showed that the serA promoter is present on this DNA fragment ( Table 5). As shown previously (43), serA was constitutively repressed in an lrp::TnJO strain. Interestingly, the serA promoter was constitutively induced in the livR strain (Table 5).…”

“…The sequence of the serA promoter has not been reported. Tuan et al (43) have shown that serA is regulated by Lrp and leucine. A segment of DNA containing serA and its natural promoter, along with a preliminary sequence of the promoter region, was obtained from G. Grant.…”

“…A role for Lrp in the induction by leucine of the tdh operon has been proposed (43). This report describes a new scheme for the isolation of mutations in a gene that encodes a trans-acting factor involved in the leucine induction of the tdh promoter.…”

“…Results from several laboratories indicate that a common trans-acting factor, encoded by a single regulatory gene, controls the expression of ilvIH (31), opp (40a), sdaA, serA, and the enzymatic activity of TDH (43). This gene, designated Irp (leucine-responsive regulatory protein), is situated at the 20-min region of the E. coli chromosome.…”

Cell division, one-carbon metabolism and methionine synthesis in a metK-deficient Escherichia coli mutant, and a role for MmuM

“…In our earlier work, we showed that expression from the metK promoter is repressed by the regulatory protein Lrp and induced by leucine, which combines with Lrp and removes it from the promoter (Tuan et al, 1990). Strain MEW402 carries the metK84 mutation, a single base pair change next to the metK promoter, and as a result greatly underproduces SAM synthase unless provided with leucine to increase metK expression (Wei & Newman, 2002).…”