Novel mechanism of catabolite repression that exists in the pentose operons of escherichia coli K-12

Abstract

During the study on transcriptional regulation of Escherichia coli K-12 ribose (rbs) operon, it was observed that the operon is repressed by the presence of D-xylose. However, the other sugars examined except D-glucose had little effect on the expression of the rbs operon and the xylose(xyl) operon was not affected by the presence of D-ribose. Genetic analysis and β-galactosidase assay revealed that XylR, a regulator of the xylose operon, was responsible for the repression. {\it E.coli} cells also showed a diauxic growth, which is typical in the catabolite repression by D-glucose, in minimal medium containing D-xylose plus D-ribose. These results led us to the conclusion that there exists novel mechanism of catabolite repression in the rbs operon that is exerted by D-xylose through the action of XylR. Furthermore, it was shown that the xyl and rbs operon were repressed by the presence of L-arabinose whereas the arabinose operon was not affected by D-xylose or D-ribose, suggesting that there exists a mechanism determining the preference of pentose utilization at the level of transcription.