Differential control by IHF and cAMP of two oppositely oriented genes, hpt and gcd, in Escherichia coli: significance of their partially overlapping regulatory elements

Abstract

The hpt gene, which encodes hypoxanthine phosphoribosyltransferase, is located next to, but transcribed in the opposite direction to, the gcd gene, which codes for a membrane-bound glucose dehydrogenase, at 3.1 min on the Escherichia coli genome. In their promoter-operator region, putative regulatory elements for integration host factor (IHF) and for the complex comprising 3', 5'-cyclic AMP (cAMP) and its receptor protein (CRP) are present, and they overlap the promoters for hpt and gcd, respectively. The involvement of IHF and cAMP-CRP, as well as the corresponding putative cis-acting elements, in the expression of the two genes was investigated by using lacZ operon fusions. In an adenylate cyclase-deficient strain, addition of cAMP increased the expression of hpt and reduced the expression of gcd. In agreement with this observation, the introduction of mutations into the putative binding element for the cAMP-CRP complex enhanced the expression of gcd. In contrast, mutations introduced into the putative IHF-binding elements increased the level of hpt expression. Similar results were obtained with IHF-defective strains. Thus, the expression of the two genes is regulated in a mutually exclusive manner. Additional experiments with mutations at the -10 sequence of the gcd promoter suggest that the binding of RNA polymerase to the hpt promoter interferes with the interaction of RNA polymerase with the gcd promoter, and vice versa.

The Escherichia coli cAMP receptor protein bound at a single target can activate transcription initiation at divergent promoters: a systematic study that exploits new promoter probe plasmids

“…CRP binds to specific 22 bp DNA sequences at target promoters and activates transcription by making direct interactions with holo RNA polymerase (RNAP). Examples where the DNA target for CRP is located between divergently transcribed genes include the rhaBAD operon encoding the enzymes for the catabolism of rhamnose [3], the cai-fix operons involved in anaerobic carnitine metabolism [4], the fucPIK-fucAO operon encoding the enzymes for utilization of fucose [5], the paa catabolic operons responsible for phenylacetic acid degradation [6], the guaBA-xseA operon encoding the enzymes involved in the metabolism of guanine nucleotide biosynthesis [7], the nagE-B operons that encode enzymes involved in the uptake and degradation of Nacetylglucosamine [8], the papI-B operon which regulates the expression of adhesive pili [9], and the hpt-gcd operon which encodes enzymes for the metabolism of hypoxanthine phosphotransferase and membrane-bound glucose dehydrogenase [10].…”

Emergent Properties in Complex Synthetic Bacterial Promoters

“…This protein is involved in step 1 of the subpathway that synthesizes IMP (Inosine monophosphate) from hypoxanthine. 35 And finally, the acs gene that is regulate by at least two CRP (activator) and three IHF (repressor). This gene encodes for acetyl-CoA synthetase.…”

“…This gene encodes for hypoxanthine phosphoribosyltransferase. This protein is involved in step 1 of the subpathway that synthesizes IMP (Inosine monophosphate) from hypoxanthine . And finally, the acs gene that is regulate by at least two CRP (activator) and three IHF (repressor).…”

New xylose transporters support the simultaneous consumption of glucose and xylose in Escherichia coli

“…When the cAMP-CRP complex is formed and binds to the promoter-operon region, operon expression is repressed because the smooth forward movement of RNA polymerase from the promoter region is limited. IHF functions as a spanner that can bend the DNA sequence 18 , causing the −10 and −35 regions to approach the binding element of the cAMP-CRP complex in space. Thus, as the cAMP-CRP complex binds the promoter operon, it blocks the −10 and −35 regions, which are key elements that RNA polymerase recognizes and binds.…”