A gyrB-like gene from the hyperthermophilic bacterion Thermotoga maritima

We have cloned and sequenced two overlapping DNA fragments (3236 bp) containing a gene encoding the ATPase subunit of a type II DNA topoisomerase from the hyperthermophilic bacterion Thermotoga maritima (Tm Top2B). The deduced protein is composed of 636 aa with a calculated molecular mass of 72415 Da. It shares significant similarities with the ATPase subunits of mesophilic bacterial DNA topoisomerases II, either DNA gyrase (GyrB) or DNA topoisomerase IV (ParE). Although the highest similarity scores are obtained with GyrB proteins (55% identity with Bacillus subtilis DNA gyrase), a detailed phylogenetic analysis of all known DNA topoisomerases II does not allow us to determine if Tm Top2B corresponds to a DNA gyrase or a DNA topoisomerase IV. This hyperthermophilic Top2B protein exhibits a larger amount of charged amino acids than its mesophilic homologues, a feature which could be important for its thermostability. No gyrA-like gene has been found near top2B. A gene coding for a transaminase B-like protein was found in the upstream region of top2B.