title: When a helicase is not a helicase: dsDNA tracking by the motor protein EcoR124I.
abstract: Using a combination of single molecule and bulk solution measurements, we have examined the DNA translocation activity of a helicase, the Type I restriction modification enzyme EcoR124I. We find that EcoR124I can translocate past covalent interstrand crosslinks, inconsistent with an obligatory unwinding mechanism. Instead, translocation of the intact dsDNA occurs principally via contacts to the sugar-phosphate backbone and bases of the 3'-5' strand; contacts to the 5'-3' strand are not essential for motion but do play a key role in stabilising the motor on the DNA. A model for dsDNA translocation is presented that could be applicable to a wide range of other enzyme complexes that are also labelled as helicases but which do not have actual unwinding activity.
authors.affiliation: DNA-Protein Interactions Unit, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol, UK.
authors.forename: Louise K
authors.initials: LK
authors.lastname: Stanley
authors.forename: Ralf
authors.initials: R
authors.lastname: Seidel
authors.forename: Carsten
authors.initials: C
authors.lastname: van der Scheer
authors.forename: Nynke H
authors.initials: NH
authors.lastname: Dekker
authors.forename: Mark D
authors.initials: MD
authors.lastname: Szczelkun
authors.forename: Cees
authors.initials: C
authors.lastname: Dekker
mesh_terms: D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism*; D015253:Deoxyribonucleases, Type I Site-Specific / Q000235:genetics / Q000378:metabolism*; D008280:Magnetics; D008957:Models, Genetic; D020409:Molecular Motor Proteins / Q000378:metabolism*; D009690:Nucleic Acid Conformation; D009711:Nucleotides / Q000378:metabolism
chemical_list: D020409:Molecular Motor Proteins; D009711:Nucleotides; D004247:DNA; C048242:endodeoxyribonuclease EcoR124I; D015253:Deoxyribonucleases, Type I Site-Specific; D004265:DNA Helicases