Cloning and sequencing of the gene (tsg56) encoding a type-specific antigen from Rickettsia tsutsugamushi

A type-specific antigen (TSA) in Rickettsia tsutsugamushi is a 56-kDa protein located on the rickettsial surface. The gene (tsg56) encoding the TSA was isolated from R. tsutsugamushi Gilliam strain. Sequencing revealed an open reading frame of 1572 bp encoding a 524-amino acid (aa) protein with an Mr of 56,053. The deduced aa sequence consists of a 22-aa signal sequence and the mature TSA sequence (502 aa; Mr 53,803), whose N-terminal portion has the aa sequence determined directly in our previous study [Ohashi et al., Infect. Immun. 57 (1989) 1427-1431]. Alternate localization of hydrophobic and hydrophilic regions was recognized in the TSA molecule, suggesting that the TSA is a transmembrane protein. The codon usage in the A + T-rich (59%) tsg56 gene reflects a high A + T content of R. tsutsugamushi. The 5'-flanking region contains sequences similar to those of ribosome-binding sites and promoters of Escherichia coli.