Molecular and functional analysis of the Rickettsia typhi groESL operon

The groESL operon from an obligate, intracellular, Gram-negative bacterium Rickettsia typhi, the etiologic agent of murine typhus, was cloned and sequenced. The sequence analysis of 2229 bp of the groESL operon reveals two open reading frames of 288 nucleotides (groES) and 1653 nucleotides (groEL) separated by 20 nucleotides. The deduced amino acid sequence of R. typhi GroES and GroEL shows a high degree of identity with other bacterial GroES and GroEL. Reverse transcriptase-polymerase chain reaction and Northern blot analysis indicated that both groES and groEL are transcribed as a single mRNA. The transcriptional start point at 81 nucleotides upstream of the groES start codon was determined by primer extension. The promoter analysis shows no regulatory CIRCE element as it is known for many Gram-positive and Gram-negative bacteria. However, it contains the sequence similar to the putative sigma(70)-dependent promoter and lacks the -35 sequence of the putative sigma(32)-dependent promoter. Complementation assay by R. typhi groESL in a temperature sensitive Escherichia coli groEL mutant restored significant growth ability at non-permissive temperature.