DNA sequencing of the gene encoding Salmonella typhimurium-derived T-cell inhibitor (STI) and characterization of the gene product, cloned STI

In a previous study, we found a novel protein which inhibited T-cell respon siveness to interleukin-2 (IL-2) in Salmonella typhimurium and called it S. typhimurium-derived T-cell inhibitor (STI). In this study, we analyzed the DNA sequence of the gene encoding STI. The STI gene was cloned into a plas mid vector, pUC118, and expressed in Escherichia coil JM109. Like native ST I, the cloned STI inhibited IL-2-dependent CTLL-2 cell growth. Furthermore, this growth inhibition involved downregulation of IL-2 receptor expression . These results indicate that the cloned STI expressed in E. coli was ident ical to native STI. Sequencing revealed that the STI gene contained an open reading frame of 2298 base pairs encoding a precursor form of 765 amino ac id residues (molecular mass 83605) that is processed into a mature form of 745 amino acid residues with molecular mass 81548. Homology analysis reveal ed that its amino acid sequence was highly homologous with that of the beta -glucosidase of E. coli K-12. We designated the gene encoding STI sti. (C) 1998 Federation of European Microbiological Societies. Published by Elsevie r Science B.V. All rights reserved.