title: The NPH-II helicase displays efficient DNA x RNA helicase activity and a pronounced purine sequence bias.
abstract: The superfamily 2 vaccinia viral helicase nucleoside triphosphate phosphohydrolase-II (NPH-II) exhibits robust RNA helicase activity but typically displays little activity on DNA substrates. NPH-II is thus believed to make primary contacts with backbone residues of an RNA substrate. We report an unusual nucleobase bias, previously unreported in any superfamily 1 or 2 helicase, whereby purines are heavily preferred as components of both RNA and DNA tracking strands. The observed sequence bias allows NPH-II to efficiently unwind a DNA x RNA hybrid containing a purine-rich DNA track derived from the 3'-untranslated region of an early vaccinia gene. These results provide insight into potential biological functions of NPH-II and the role of sequence in targeting NPH-II to appropriate substrates. Furthermore, they demonstrate that in addition to backbone contacts, nucleotide bases play an important role in modulating the behavior of NPH-II. They also establish that processive helicase enzymes can display sequence selectivity.
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: Sean David
authors.initials: SD
authors.lastname: Taylor
authors.forename: Amanda
authors.initials: A
authors.lastname: Solem
authors.forename: Jane
authors.initials: J
authors.lastname: Kawaoka
authors.forename: Anna Marie
authors.initials: AM
authors.lastname: Pyle
mesh_terms: D001483:Base Sequence; D004247:DNA / Q000737:chemistry*; D005821:Genetic Techniques; D007700:Kinetics; D008969:Molecular Sequence Data; D009696:Nucleic Acids / Q000737:chemistry; D043583:Nucleoside-Triphosphatase / Q000378:metabolism*; D011506:Proteins / Q000737:chemistry; D011687:Purines / Q000737:chemistry*; D011743:Pyrimidines / Q000737:chemistry; D020365:RNA Helicases / Q000378:metabolism*; D013379:Substrate Specificity; D014616:Vaccinia virus / Q000201:enzymology
chemical_list: D009696:Nucleic Acids; D011506:Proteins; D011687:Purines; D011743:Pyrimidines; D004247:DNA; D043583:Nucleoside-Triphosphatase; D020365:RNA Helicases; C030985:purine