title: Molecular mechanism of resolving trinucleotide repeat hairpin by helicases.
abstract: Trinucleotide repeat (TNR) expansion is the root cause for many known congenital neurological and muscular disorders in human including Huntington's disease, fragile X syndrome, and Friedreich's ataxia. The stable secondary hairpin structures formed by TNR may trigger fork stalling during replication, causing DNA polymerase slippage and TNR expansion. Srs2 and Sgs1 are two helicases in yeast that resolve TNR hairpins during DNA replication and prevent genome expansion. Using single-molecule fluorescence, we investigated the unwinding mechanism by which Srs2 and Sgs1 resolves TNR hairpin and compared it with unwinding of duplex DNA. While Sgs1 unwinds both structures indiscriminately, Srs2 displays repetitive unfolding of TNR hairpin without fully unwinding it. Such activity of Srs2 shows dependence on the folding strength and the total length of TNR hairpin. Our results reveal a disparate molecular mechanism of Srs2 and Sgs1 that may contribute differently to efficient resolving of the TNR hairpin.
authors.affiliation: Bioengineering Department, University of Illinois, 1304 West Springfield Avenue, Urbana, IL 61801, USA.
authors.forename: Yupeng
authors.initials: Y
authors.lastname: Qiu
authors.affiliation: Department of Molecular Biophysics and Biochemistry, Yale University, 333 Cedar Street, PO Box 208024, New Haven, CT 06520, USA.
authors.forename: Hengyao
authors.initials: H
authors.lastname: Niu
authors.affiliation: Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA; Physics Frontier Center (Center of Physics for Living Cells), University of Illinois, 1110 West Green Street, Urbana, IL 61801, USA.
authors.forename: Lela
authors.initials: L
authors.lastname: Vukovic
authors.affiliation: Department of Molecular Biophysics and Biochemistry, Yale University, 333 Cedar Street, PO Box 208024, New Haven, CT 06520, USA.
authors.forename: Patrick
authors.initials: P
authors.lastname: Sung
authors.affiliation: Bioengineering Department, University of Illinois, 1304 West Springfield Avenue, Urbana, IL 61801, USA; Institute for Genomic Biology, University of Illinois, 1206 West Gregory Street, Urbana, IL 61801, USA; Physics Frontier Center (Center of Physics for Living Cells), University of Illinois, 1110 West Green Street, Urbana, IL 61801, USA; Biophysics and Computational Biology, University of Illinois, 1110 West Green Street, Urbana, IL 61801, USA. Electronic address: smyong@illinois.edu.
authors.forename: Sua
authors.initials: S
authors.lastname: Myong
mesh_terms: D004265:DNA Helicases / Q000378:metabolism*; D005453:Fluorescence; D031541:Fluorescence Resonance Energy Transfer; D055029:Inverted Repeat Sequences / Q000235:genetics*; D008958:Models, Molecular; D011487:Protein Conformation; D058767:Protein Unfolding; D053484:RecQ Helicases / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D018911:Trinucleotide Repeats / Q000235:genetics*
chemical_list: D029701:Saccharomyces cerevisiae Proteins; C061376:SRS2 protein, S cerevisiae; C090472:SGS1 protein, S cerevisiae; D004265:DNA Helicases; D053484:RecQ Helicases