Characterization of the gene encoding the protective paracrystalline-surface-layer protein of Rickettsia prowazekii: presence of a truncated identical homolog in Rickettsia typhi.

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Abstract
The DNA sequence of the gene encoding the protective surface protein antigen (SPA) of Rickettsia prowazekii has been determined. The open reading frame of 4836 nucleotides with promoter and ribosome-binding site is present on a 10.1-kilobase EcoRI fragment. The encoded carboxyl terminus of the 169-kDa protein contains a potential transmembrane region and hydrophilic regions with many lysine and arginine residues potentially accessible to proteolytic cleavage. Because the rickettsia-derived SPA has an estimated molecular mass of only 120 kDa and does not contain several predicted large carboxyl-region CNBr fragments, the SPA product appears to be processed by the rickettsiae. Eight other CNBr fragments were identical in sequence to those predicted from the encoded gene. A complementary 8.7-kilobase EcoRI fragment of Rickettsia typhi DNA was cloned. This fragment lacked a 1433-base-pair region that included the promoter, ribosome-binding site, and the initial 1162 base pairs of the open reading frame encoding the R. prowazekii SPA but had a 3674-base-pair region identical with the remainder of the R. prowazekii SPA gene sequence.