Identification of the Chlamydia trachomatis RecA-encoding gene

DNA sequencing of the major outer membrane protein (MOMP) gene (omp1) from Chlamydia trachomatis shows that some strains have a mosaic structure suggestive of homologous recombination between two distinct omp1 genes. On the basis of this conjecture, we attempted to clone by complementation and sequence the chlamydial recA homolog from C. trachomatis serovar L2. Chlamydial genomic DNA was partially restricted with XbaI, and fragments of 2 to 4 kb were ligated into pUC19. The recombinant plasmid was electroporated into Escherichia coli HB101 (RecA-), and colonies were selected in the presence of methyl methanesulfonate (MMS). A 2.1-kb fragment of C. trachomatis DNA in pUC19 conferred relative MMS resistance to E. coli HB101. When this recombinant plasmid (pX203) was electroporated into E. coli JC14604 (RecA- lacZ), lac+ recombinants were isolated. Rabbit polyclonal antibodies produced to purified E. coli RecA were immunoreactive in an immunoblot assay with a 35-kDa antigen in RecA- strains of E. coli transformed with pX203. The 2.1-kb insert was cycle sequenced by the dideoxy chain termination method. An open reading frame of 1,056 bp encoding 352 amino acids that had 44% sequence identity with E. coli RecA was identified. The finding of a recA homolog in C. trachomatis suggests that homologous recombination may occur in this organism. The cloned C. trachomatis RecA-encoding gene will be useful for the construction of a recA mutant once a gene transfer system is developed for chlamydiae.