ANNEALING OF COMPLEMENTARY-DNA STRANDS ABOVE THE MELTING-POINT OF THEDUPLEX PROMOTED BY AN ARCHAEAL PROTEIN

One enigma in the biology of hyperthermophilic microorganisms, living near or above 100 degrees C, is how their genomes can be stable and, a t the same time, plastic at temperatures above the melting point. The nonspecific DNA-binding protein Sso7d of the hyperthermophilic archaeo n Sulfolobus solfataricus is known to protect DNA from thermal denatur ation. We report here that Sso7d promotes the renaturation of compleme ntary DNA strands at temperatures above the melting point of the duple x. This novel annealing activity is strictly homology-dependent, and e ven one mismatch in a stretch of 17 complementary bases severely reduc es its efficiency. Since pairing of homologous single strands is a key step in all fundamental processes involving nucleic acids, such as tr anscription, replication, recombination, and repair, Sso7d is a candid ate component of the protein machinery devoted to the coupling of DNA stability to metabolic flexibility at high temperature. (C) 1997 Acade mic Press Limited.