Nucleic Acids Research Advance Access originally published online on August 24, 2007
Nucleic Acids Research 2007 35(17):5809-5818; doi:10.1093/nar/gkm613
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Nucleic Acids Research, 2007, Vol. 35, No. 17 5809-5818
© 2007 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Nucleic Acid Enzymes |
The yeast Pif1p DNA helicase preferentially unwinds RNA–DNA substrates
Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
*To whom correspondence should be addressed. Tel: +1 609 258 2723; Fax: +1 609 258 1701; Email: jboule{at}princeton.edu
Received March 29, 2007. Revised July 24, 2007. Accepted July 26, 2007.
Pif1p is the prototypical member of the PIF1 family of DNA helicases, a subfamily of SFI helicases conserved from yeast to humans. Baker's yeast Pif1p is involved in the maintenance of mitochondrial, ribosomal and telomeric DNA and may also have a general role in chromosomal replication by affecting Okazaki fragment maturation. Here we investigate the substrate preferences for Pif1p. The enzyme was preferentially active on RNA–DNA hybrids, as seen by faster unwinding rates on RNA–DNA hybrids compared to DNA–DNA hybrids. When using forked substrates, which have been shown previously to stimulate the enzyme, Pif1p demonstrated a preference for RNA–DNA hybrids. This preferential unwinding could not be correlated to preferential binding of Pif1p to the substrates that were the most readily unwound. Although the addition of the single-strand DNA-binding protein replication protein A (RPA) stimulated the helicase reaction on all substrates, it did not diminish the preference of Pif1p for RNA–DNA substrates. Thus, forked RNA–DNA substrates are the favored substrates for Pif1p in vitro. We discuss these findings in terms of the known biological roles of the enzyme.
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