Plasmid pGS5 from the hyperthermophilic archaeon Archaeaglobus profundus is negatively supercoiled

We present evidence that, in contrast to plasmids from other hyperthermophi lic archaea, which are in the relaxed to positively supercoiled state, plas mid pGS5 (2.8 kb) from Archaeoglobus profundus is negatively supercoiled. T his might be due to the presence of a gyrase introducing negative supercoil s, since gyrase genes are present in the genome of its close relative A. fu lgidus, and suggests that gyrase activity predominates over reverse gyrase whenever the two topoisomerases coexist in cells.