Cloning, expression and sequence analysis of the gene encoding the 120kD surface‐exposed protein of Rickettsia rickettsii

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Abstract
Rickettsia rickettsii (R strain) genomic DNA was partially digested and cloned into the lambda expression vector gt11 generating a genomic clone bank. Trans-formant plaques were screened with antisera generated against the 120 kiloDalton protein of R. rickettsii to detect those phage expressing the recombinant protein. The gene encoding the 120kD protein was localized to a 4.3 kilobase Sphl-BamHl fragment from the recombinant phage and subcioned into pUC18 and pUC19. Full-length expression of the recombinant protein was achieved with both orientations. The gene and flanking regions were sequenced. The p120 gene consists of 3900 base pairs coding for 1300 amino acids. A distinguishable promoter region was not identified, although there are several 5′ sequences that resemble classical prokaryotic promoters. Downstream of the termination codon for this gene lies a 726 base pair open reading frame on the opposite strand with the potential to encode a protein of approximately 27 kD. The identity of this putative gene product is unknown. The two open reading frames are separated by a 106 base pair intergenic region that consists of a stretch of dyad symmetry resembling rho-independent transcriptional terminators.