Elongation Factor Ts ofChlamydia trachomatis:Structure of the Gene and Properties of the Protein

A putative structural gene cluster containing four open reading frames (ORFs) located downstream of theomp1gene ofChlamydia trachomatismouse pneumonitis (MoPn) was cloned and sequenced. A GenBank survey indicated that the identified cluster is similar to therpsB-tsf-pyrH(smbA)-frrregion ofEscherichia coli.The second ORF was 846 bp encoding a 282-amino-acid polypeptide with a calculatedMr30,824. Alignment of this deduced protein sequence andE. colielongation factor Ts (EF-Ts, product oftsf) demonstrated 34% identity and an additional 14% similarity. The putative chlamydialtsfgene was expressed inE. colias a nonfusion protein and as a 6× His-tagged fusion protein. By SDS–PAGE analysis, the molecular weights of the nonfusion recombinant protein and a protein of chlamydial elementary bodies (EBs), which was recognized by monoclonal antibodies derived from the nonfusion recombinant protein, are 34 kDa. The purified recombinant 6× His-tagged fusion protein increased the rate of GDP exchange with bothChlamydiaandE. colielongation factor Tu (EF-Tu). These data show that the second gene of the identified cluster istsf.Unlike EF-Ts from any other species, its activity was comparable to that ofE. coliEF-Ts in exchange reaction withE. coliEF-Tu.