title: DNA-dependent ATPase activity of bacterial XPB helicases.
abstract: XPB, the largest subunit of the eukaryotic transcription factor TFIIH, is essential for both initiation of transcription by RNA polymerase II and nucleotide excision repair (NER). XPB belongs to the SF2 superfamily of monomeric helicases. XPB helicase is thought to have evolved in eukaryotes; however, a gene highly homologous to human XPB can be found in a number of bacteria. This report is the first biochemical characterization of XPB homologues from bacteria, specifically those from Mycobacterium tuberculosis and Kineococcus radiotolerans. Similarly to eukaryotic XPB, bacterial XPB are ATP-dependent 3' --> 5' DNA helicases. The ATPase activity of these XPB helicases is DNA-dependent, requiring a minimum of 4-nucleotide long single-stranded DNA (ssDNA). The maximum rates of ATP hydrolysis are about 10 and 50 molecules per minute by one XPB monomer on a 21-nucleotide ssDNA oligomer and on 5-kb long circular ssDNA, respectively. The ATP hydrolysis by the bacterial XPBs is coupled to their translocation along single-stranded DNA. The hydrolytic activity is strongly dependent on both the nature of a nucleotide triphosphate and that of a divalent metal. The inefficient ATP hydrolysis by bacterial XPB is consistent with nonprocessive functions of its eukaryotic homologue in locally remodeling DNA during transcription initiation and NER.
authors.affiliation: Department of Medicinal Chemistry, College of Pharmacy, University of Michigan, Ann Arbor, Michigan 48109-1065, USA.
authors.forename: Tapan
authors.initials: T
authors.lastname: Biswas
authors.forename: Jessica M
authors.initials: JM
authors.lastname: Pero
authors.forename: Caleb G
authors.initials: CG
authors.lastname: Joseph
authors.forename: Oleg V
authors.initials: OV
authors.lastname: Tsodikov
mesh_terms: D000192:Actinomycetales / Q000201:enzymology / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D003001:Cloning, Molecular; D004265:DNA Helicases / Q000737:chemistry / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D009169:Mycobacterium tuberculosis / Q000201:enzymology / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D000251:Adenosine Triphosphatases; D004265:DNA Helicases