Sequence, transcriptional analysis and chromosomal location of the Xanthomonas campestris pv. campestris uvrB gene.

The uvrB gene of Xanthomonas campestris pv. campestris, a Gram-negative plant pathogenic bacterium inhabiting soil and infected plants, was cloned and sequenced. This gene has the capacity to encode a polypeptide of 673 amino acid residues with a calculated molecular mass of 75.9 kDa. Its deduced amino acid sequence shows a high degree of similarity and possesses domain conservation to those of bacterial UvrB. The uvrB mutant, isolated by gene replacement, is extremely sensitive to ultraviolet irradiation. Like the situation in the X. campestris pv. campestris recA gene, no SOS box is present upstream of the uvrB gene. Northern blotting and transcriptional fusion assay with lacZ indicated that X. campestris pv. campestris uvrB is expressed constitutively at high levels and cannot be further induced by UV irradiation. These results suggest a regulatory mechanism different from that for the expression of Escherichia coli uvrB. Using a gene-tagging strategy in conjunction with pulsed-field gel electrophoresis, the uvrB gene was located near 1 o'clock on the X. campestris pv. campestris 17 chromosome (4.8 Mb) map, which is far apart from the lexA-recA-recX cluster near 5 o'clock.