GENETIC AND MOLECULAR ANALYSIS OF THE TRANSFER-RNA-TUFB OPERON OF THEMYXOBACTERIUM STIGMATELLA-AURANTIACA

The tufB gene, encoding elongation factor Tu (EF-Tu), from the myxobac terium Stigmatella aurantiaca was cloned and sequenced. It is preceded by four tRNA genes, the first ever described in myxobacteria. The tRN A synthesized from these genes and the general organization of the loc us seem identical to that of Escherichia coli, but differences of pote ntial importance were found in the tRNA sequences and in the intergeni c regions, The primary structure of EF-Tu was deduced from the tufB DM A sequence. The factor is composed of 396 amino acids, with a predicte d molecular mass of 43.4 kDa, which was confirmed by expression of tuf B in maxicells. Sequence comparisons between S.aurantiaca EF-Tu and ot her bacterial homologues from E.coli, Salmonella typhimurium and Therm us thermophilus displayed extensive homologies (75.9%), Among the vari able positions, two Cys residues probably involved in the temperature sensitivity of E.coli and S.typhimurium EF-Tu are replaced in T.thermo philus and S.aurantiaca EF-Tu. Since two or even three tuf genes have been described in other bacterial species, the presence of multiple tu f genes was sought for, Southern and Northern analysis are consistent with two tuf genes in the genome of S.aurantiaca, Primer extension exp eriments indicate that the four tRNA genes and tufB are organized in a single operon.