Reverse gyrase hyperthermophiles

Thermostabilization of double-stranded DNA is provided by base pairing (1) and base stacking (see Reference 27 and references therein) complemented by positive supercoiling by reverse gyrase [in hyperthermophiles (8, 9, 28)] and by stabilization via interactions with histone-like proteins (29, 30). The relative contribution of base paring and base stacking into the thermostability of double-stranded DNA has been a subject of extensive studies for more than four decades (1, 27, 31). We will consider here this question, based on the results of recent experimental and computational works (31, 32). 

The unique enzymatic activity of reverses gyrases, i.e., the efficient production of positively supercoiled DNA, was used by a number of authors to estimate the impact of such a DNA structure on various biological mechanisms. These include chromatin stability,recombination, and transcription. However, the in vivo role of reverse gyrases in hyperthermophiles remains a matter of speculation. It was suggested long ago that one of the main functions of topoisomerases is to tightly... 

Fig, 6. DNA topology in hyperthermophiles. The dashed arrows for topo III (A) and reverse gyrase (B) indicate that this activity is presumably not a major determinant of the supercoiling density. 

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