DNA Repair Enzymes in Hyperthermophilic Archaea

Abstract

The presence of hyperthermophilic microorganisms in hydrothermal environments at temperatures above 90°C is now well established (Stetter, 1990). In fact, isolates from deep sea marine hydrothermal vents can grow optimally under pressure at temperatures up to 113°C (Blochl et al., 1997). Most of the hyperthermophiles are members of the Domain Archaea as defined by Woese et al. (1990), and their existence raises the question of how metabolic processes are sustained at extremely high temperatures. Not surprisingly, all of the enzymes isolated to date from hyperthermophiles display unusual thermostability (Adams, 1993; DiRuggiero and Robb, 1996), however, temperature in the region of 100°C greatly accelerate the spontaneous chemical degradation of DNA by orders of magnitude (Lindahl, 1993). Despite this, hyperthermophiles such as Pyrococcus furiosus are capable of rapid growth at or near to 100°C (Fiala and Stetter, 1986) and apparently maintain a normal level of genetic stability (Brown et al., 1994; Keeling and Doolittle, 1995). We suggest that efficient DNA repair and replication mechanisms are a prerequisite for growth and survival of these microorganisms, yet these processes remain largely unexplored. Further, despite extensive sequencing of Archaeal genomes and the recent publication of the complete genome sequence of the methanogen Methanococcus jannaschii (Bult et al., 1996) very little is known of the proteins involved in DNA repair and replication in hyperthermophilic Archaea.