When a helicase is not a helicase: dsDNA tracking by the motor protein EcoR124I.
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.
Stanley
Louise K
LK
DNA-Protein Interactions Unit, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol, UK.
Seidel
Ralf
R
van der Scheer
Carsten
C
Dekker
Nynke H
NH
Szczelkun
Mark D
MD
Dekker
Cees
C
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
D020409:Molecular Motor Proteins; D009711:Nucleotides; D004247:DNA; C048242:endodeoxyribonuclease EcoR124I; D015253:Deoxyribonucleases, Type I Site-Specific; D004265:DNA Helicases