Characterization of Xanthomonas oryzae pv. oryzae recX, a gene that is required for high-level expression of recA

Analysis of the nucleotide sequence downstream from the Xanthomonas oryzae pv, oryzae recA gene reveals two orfs designated orfX and recX. The former has the potential to code for a 5.6 kDa protein of unknown function while t he latter encodes for a putative 14.6 kDa protein with homology to RecX fro m various bacteria. Northern blot analysis and RT-PCR results show that rec A-orfX-recX are coregulated and arranged in an operon, A recX mutant was co nstructed. The mutant has no obvious growth defects or stress response defe cts, except that it cannot support high-level expression of recA from an ex pression vector. Introduction of the plasmid containing recA into the recX mutant resulted in reduced transformation efficiency and ail transformants tested had mutations with reduced RecA levels, Moreover, the recX mutant ha s reduced basal levels of RecA. This has not been observed in other bacteri a. When inactivated recX was complemented in trans, both changes were rever sed. recX mutation has no effect on the regulation of the recA promoter, su ggesting that its effect on the RecA level could be post-transcriptional. ( C) 2001 Federation of European Microbiological Societies. Published by Else vier Science B.V. All rights reserved.