title: Escherichia coli DNA helicase II is active as a monomer.
abstract: Helicases are thought to function as oligomers (generally dimers or hexamers). Here we demonstrate that although Escherichia coli DNA helicase II (UvrD) is capable of dimerization as evidenced by a positive interaction in the yeast two-hybrid system, gel filtration chromatography, and equilibrium sedimentation ultracentrifugation (Kd = 3.4 microM), the protein is active in vivo and in vitro as a monomer. A mutant lacking the C-terminal 40 amino acids (UvrDDelta40C) failed to dimerize and yet was as active as the wild-type protein in ATP hydrolysis and helicase assays. In addition, the uvrDDelta40C allele fully complemented the loss of helicase II in both methyl-directed mismatch repair and excision repair of pyrimidine dimers. Biochemical inhibition experiments using wild-type UvrD and inactive UvrD point mutants provided further evidence for a functional monomer. This investigation provides the first direct demonstration of an active monomeric helicase, and a model for DNA unwinding by a monomer is presented.
authors.affiliation: Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
authors.forename: L E
authors.initials: LE
authors.lastname: Mechanic
authors.forename: M C
authors.initials: MC
authors.lastname: Hall
authors.forename: S W
authors.initials: SW
authors.lastname: Matson
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D002850:Chromatography, Gel; D004265:DNA Helicases; D017931:DNA Primers; D004260:DNA Repair; D004277:DNA, Single-Stranded / Q000378:metabolism; D019281:Dimerization; D004789:Enzyme Activation; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D011485:Protein Binding
chemical_list: D017931:DNA Primers; D004277:DNA, Single-Stranded; D029968:Escherichia coli Proteins; D000251:Adenosine Triphosphatases; C506746:UvrD protein, E coli; D004265:DNA Helicases