Open AccessA fluorescence-based assay for monitoring helicase activity.
Author(s) -
Kevin D. Raney,
Lawrence C. Sowers,
David P. Millar,
Stephen J. Benkovic
Publication year - 1994
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.91.14.6644
Subject(s) - helicase , fluorescence , oligonucleotide , duplex (building) , dna , biophysics , chemistry , substrate (aquarium) , thymine , microbiology and biotechnology , biochemistry , biology , rna , physics , gene , ecology , quantum mechanics
A continuous fluorescence-based assay is described for measuring helicase-mediated unwinding of duplex DNA. The assay utilizes an oligonucleotide substrate containing the fluorescent adenine analog, 2-aminopurine, at regular intervals. 2-Aminopurine forms a Watson-Crick-type base pair with thymine and does not distort normal B-form DNA. Fluorescence of the 2-aminopurines within this oligonucleotide is quenched 2-fold upon its hybridization to a complementary strand. Unwinding of this substrate by the T4 dda helicase restores the fluorescence of the 2-aminopurines and is easily followed using stopped-flow or steady-state fluorescence spectroscopy. The flourescence-based assay provides rate data comparable to that obtained from conventional discontinuous assays using labeled substrates and additionally furnishes a means for following a single turnover. This assay should prove useful for defining the mechanism by which helicases unwind duplex DNA.