title: The archaeal XPB protein is a ssDNA-dependent ATPase with a novel partner.
abstract: XPB is a superfamily 2 helicase with a 3'-5' polarity. In eukaryotes, XPB is an integral subunit of the transcription factor TFIIH, which plays a dual role in DNA opening at RNA polymerase II promoters and in establishing the repair bubble around a DNA lesion in nucleotide excision repair. Eukaryotic XPB has only very limited helicase activity in vitro and may function as a DNA-dependent molecular switch to catalyse local distortion of DNA in transcription and repair. Most archaea have one or two homologues of the XPB protein with a presumed role in DNA repair, but only one other subunit of the TFIIH complex, the 5'-3' helicase XPD, has been identified in archaea. Here we report the biochemical characterisation of the two homologous XPB proteins from the crenarchaeon Sulfolobus solfataricus. Although both proteins are single-stranded-DNA-stimulated ATPases, neither displays any helicase activity in vitro, consistent with recent studies of eukaryotic XPB. In almost all archaeal genomes, the xpb gene lies adjacent to a conserved partner gene, and we demonstrate that these two gene products form a physical interaction in vitro. We propose the name Bax1 (Binds archaeal XPB) for this protein, which has a predicted endonuclease domain. XPB and Bax1 may collaborate in processing nucleic acid in an archaeal-specific DNA repair pathway.
authors.affiliation: St. Andrews University, Centre for Biomolecular Sciences, North Haugh, St. Andrews, Fife KY16 9ST, UK.
authors.forename: Jodi D
authors.initials: JD
authors.lastname: Richards
authors.forename: Liza
authors.initials: L
authors.lastname: Cubeddu
authors.forename: Jennifer
authors.initials: J
authors.lastname: Roberts
authors.forename: Huanting
authors.initials: H
authors.lastname: Liu
authors.forename: Malcolm F
authors.initials: MF
authors.lastname: White
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D019843:Archaeal Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D004260:DNA Repair; D011485:Protein Binding; D048229:Sulfolobus solfataricus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D019843:Archaeal Proteins; D000251:Adenosine Triphosphatases; C037693:single stranded DNA dependent ATPase