Molecular basis for modulated regulation of gene expression in the arginine regulon ofEscherichia coliK-12

Abstract
We compare the nucleotide sequences of the regulatory regions of five genes or groups of genes of the arginine regulon of Escherichia coli K-12 : argF, argI, argR, the bipolar argECBH operon and the carAB operon. All these regions harbour one or two copies of a conserved 18 bp sequence which appears to constitute the basic arginine operator sequence (ARG box) . We discuss the influence of ARG box copy number, degree of dyad symmetry, base composition, and position relative to the cognate promoter site on the derepression-repression ratios of the genes of the regulon. A novel hypothesis, based on structural considerations, is also put forward to account for the absence ot attenuation control.