IDENTIFICATION OF THE CHLAMYDIA-TRACHOMATIS RECA-ENCODING GENE

DNA sequencing of the major outer membrane protein (MOMP) gene (ompl) from Chlamydia trachomatis shows that some strains have a mosaic struc ture suggestive of homologous recombination between two distinct ompl genes. On the basis of this conjecture, we attempted to clone by compl ementation and sequence the chlamydial recA homolog from C. trachomati s serovar L(2). Chlamydial genomic DNA was partially restricted with X baI, and fragments of 2 to 4 kb were ligated into pUC19. The recombina nt plasmid was electroporated into Escherichia coli HB101 (RecA(-)), a nd colonies were selected in the presence of methyl methanesulfonate ( MMS). A 2.1-kb fragment of C. trachomatis DNA in pUC19 conferred relat ive MMS resistance to E. coli HB101. When this recombinant plasmid (pX 203) was electroporated into E. coli JC14604 (RecA(-) lacZ), lac recom binants were isolated. Rabbit polyclonal antibodies produced to purifi ed E. coli RecA were immunoreactive in an immunoblot assay with a 35-k Da antigen in RecA(-) strains of E. coli transformed with pX203. The 2 .1-Kb insert was cycle sequenced by the dideoxy chain termination meth od. An open reading frame of 1,056 bp encoding 352 amino acids that ha d 44% sequence identity with E. coli RecA was identified. The finding of a recA homolog in C. trachomatis suggests that homologous recombina tion may occur in this organism. The cloned C. trachomatis RecA-encodi ng gene will be useful for the construction of a recA mutant once a ge ne transfer system is developed for chlamydiae.