DNA topology and the thermal stress response, a tale from mesophiles and hyperthermophiles

During heat shock and cold shock, plasmid DNA supercoiling changes transien tly both in mesophilic bacteria and in hyperthermophilic archaea, despite a different overall topology (negative supercoiling Versus relaxation to pos itive supercoiling). Transient changes in DNA supercoiling might be essenti al to generate the stress response, but they could also be a consequence of the physical effects of temperature on cellular components. Indeed, both a ppear intertwined. Comparison of the mechanisms acting in the two biologica l systems suggests that the dependence on temperature of the activity of di fferent DNA topoisomerases, as well as of protein binding, are key factors for the control of DNA topology during stress, which may in turn be relevan t for the expression of stress-induced genes. (C) 2000 John Wiley & Sons, I nc.