Genetic evidence of a novel ribose transport system in escherichia coli K-12

Abstract

Ribose is transported through three known sugar transporters; the rbs operon (high-affinity D-ribose transporter), the als operon(D-allose transporter) and the xyl operon(D-xylose transporter). Mutations enhancing growth arise spontaneously at the frequencies of $10^{-8} - 10^{-9}$ in ribose minimal plate from the strain lacking the rbs transport system. Genetic analysis revealed that their growth phenotypes were not dependent on the three known mechanisms and that rbsD and rbsK, the components of rbs operon, were essential. Growth of the mutants on D-ribose medium showed that their growth rates were about 80% of that of wild type with the intact rbs system. Although ribose uptake rate of the mutant was much lower than that of binding protein dependent transporter, the mutant showed better uptake rate than those of als operon and xyl operon. Genetic tagging and mapping analyses revealed that two loci from the E.coli linkage map are involved in the novel ribose transport mechanism. One was found at 25 min and the other was at 36min of E.coli strain OW1.