As all cells have to maintain their genomes intact, all organisms and particularly those that thrive under extreme conditions contain several nucleases that are required for the processing and reparation of DNA damage. Recently, several new nucleases have been identified in bacteria and eukarya (Aravind et al.
). These nucleases function either in association with DNA polymerase or autonomously and are often involved in improving the fidelity of the replisome. One of the best studied nucleases is the RecB protein, which is associated with the RecBCD complex in Escherichia coli
. This complex participates in the repair of double-strand breaks by homologous recombination. Recent structural studies (Singleton et al.
) have indicated that the RecC subunit of this complex creates a fork structure that separates the DNA strands and directs them towards the active site of the RecB nuclease (exonuclease V family; Shevelev & Hubscher, 2002
Although archaea do not seem to contain the RecBCD complex, many archaeal genomes encode proteins that have been annotated as ‘predicted nuclease of the RecB family’ (Aravind et al.
; Kinch et al.
). In the genome of Pyrococcus abyssi
, a hyperthermophilic euryarchaeon, one of these putative nucleases is encoded by the open reading frame PAB2263
. Preliminary studies indicate that PAB2263 is an exonuclease (data not shown). It is also of note that PAB2263 and its orthologues are a part of a superfamily that, in addition to RecB nucleases, includes several restriction endonucleases, archaeal Holliday junction resolvase and XPF/Rad1/Mus81 nuclease. Many of these proteins contain (GV)hhD and (DE)hK signatures and a conserved tyrosine near the C-terminus (Wang et al.
) that presumably participate in DNA degradation. However, the lack of readily detectable sequence similarity outside of their active sites has complicated their characterization and functional annotation.
To provide a structural description of these nuclease families, we have overexpressed, purified and crystallized PAB2263 from P. abyssi and collected preliminary diffraction data from these crystals. This study is motivated by the belief that structural analysis of this putative nuclease will help in understanding the functional role of this protein in cellular physiology.