Resistance to ultraviolet light in Pseudomonas syringae: sequence and functional analysis of the plasmid-encoded rulAB genes.

The indigenous plasmids, pPSR1 and pPSR5, were each shown to confer resistance to ultraviolet light (UV) in Pseudomonas syringae (Ps) pv. syringae FF5. The UV-resistance (UVR) determinant was subcloned from a cosmid library of pPSR1, and sequence analysis revealed the presence of two ORFs, designated rulAB which are homologous to the Escherichia coli umuDC mutagenic DNA repair systems and other plasmid-encoded UVR operons. Amino acid (aa) alignments indicated that RulAB are most closely related to the RumAB proteins from plasmid R391, sharing 40.5% and 48.6% aa identity with RumA and RumB, respectively. UV sensitivity assays with the cloned rulAB genes indicated that the expression of UVR in Ps required a functional recA gene.