title: Human DNA polymerase iota incorporates dCTP opposite template G via a G.C + Hoogsteen base pair.
abstract: Human DNA polymerase iota (hPoliota), a member of the Y family of DNA polymerases, differs in remarkable ways from other DNA polymerases, incorporating correct nucleotides opposite template purines with a much higher efficiency and fidelity than opposite template pyrimidines. We present here the crystal structure of hPoliota bound to template G and incoming dCTP, which reveals a G.C + Hoogsteen base pair in a DNA polymerase active site. We show that the hPoliota active site has evolved to favor Hoogsteen base pairing, wherein the template sugar is fixed in a cavity that reduces the C1'-C1' distance across the nascent base pair from approximately 10.5 A in other DNA polymerases to 8.6 A in hPoliota. The rotation of G from anti to syn is then largely in response to this curtailed C1'-C1' distance. A G.C+ Hoogsteen base pair suggests a specific mechanism for hPoliota's ability to bypass N(2)-adducted guanines that obstruct replication.
authors.affiliation: Structural Biology Program, Department of Physiology and Biophysics, Mount Sinai School of Medicine, Box 1677, 1425 Madison Avenue, New York, New York 10029, USA.
authors.forename: Deepak T
authors.initials: DT
authors.lastname: Nair
authors.forename: Robert E
authors.initials: RE
authors.lastname: Johnson
authors.forename: Louise
authors.initials: L
authors.lastname: Prakash
authors.forename: Satya
authors.initials: S
authors.lastname: Prakash
authors.forename: Aneel K
authors.initials: AK
authors.lastname: Aggarwal
mesh_terms: D001482:Base Composition; D020029:Base Pairing; D001665:Binding Sites; D002384:Catalysis; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism*; D003845:Deoxycytosine Nucleotides / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012399:Rotation; D013059:Spectrum Analysis, Raman; D013698:Templates, Genetic; D000094769:DNA Polymerase iota
chemical_list: D003845:Deoxycytosine Nucleotides; C024107:2'-deoxycytidine 5'-triphosphate; D004259:DNA-Directed DNA Polymerase; D000094769:DNA Polymerase iota; C000722070:POLI protein, human