THE RNA-POLYMERASE OF CHLAMYDIA-TRACHOMATIS HAS A FLEXIBLE SEQUENCE REQUIREMENT AT THE -10 AND -35 BOXES OF ITS PROMOTERS

Mutated variants of the predicted promoter of the countertranscript of the Chlamydia trachomatis plasmid were tested by in vitro transcripti on with chlamydial extract. A 3-bp deletion within the -10 region of t he putative promoter caused the RNA polymerase to initiate transcripti on 3 bases downstream. Many single mutations in the -10 and -35 region s did not alter promoter function. However, some multiple mutations in both hexamers rendered the promoter inefficient or ineffective. Taken together, these results indicate that (i) the sequence requirement fo r chlamydial promoters differs from that for Escherichia coli and (ii) chlamydial RNA polymerase can tolerate considerably more variation at the -10 and -35 regions. These results are paradoxical considering th e homology between C. trachomatis sigma(66) and E. coli sigma(70).