Replication protein A induces the unwinding of long double-stranded DNA regions.
We have investigated nucleoprotein filaments composed of human replication protein A (RPA) and DNA by electron microscopy. At low ionic strengths, RPA complexes with single-stranded DNA are similar in length to protein-free DNA suggesting that RPA-bound DNA remains in an extended configuration under these conditions. However, severe compaction of RPA-DNA complexes occurs in buffers with > 2 mM MgCl2 or with 100 mM NaCl. At low ionic strengths, RPA binds to A + T-rich internal regions of linear double-stranded simian virus 40 (SV40) DNA and induces separation of complementary DNA strands. RPA also binds to closed-circular SV40 DNA, but requires the function of a DNA topoisomerase to invade and completely unwind duplex DNA regions. The ability of RPA to unwind long stretches of double-stranded DNA is not shared by the bacterial single-strand binding protein and the phage T4 gene 32 protein.
Treuner
K
K
Division of Biology, Universität Konstanz, Germany.
Ramsperger
U
U
Knippers
R
R
D017104:Bacteriophage M13 / Q000235:genetics; D004247:DNA / Q000737:chemistry* / Q000378:metabolism; D004270:DNA, Circular / Q000737:chemistry / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000737:chemistry / Q000378:metabolism; D004279:DNA, Viral / Q000737:chemistry / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008854:Microscopy, Electron; D008954:Models, Biological; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D051716:Replication Protein A; D013539:Simian virus 40 / Q000235:genetics
D004270:DNA, Circular; D004277:DNA, Single-Stranded; D004279:DNA, Viral; D004268:DNA-Binding Proteins; C497167:RPA1 protein, human; D051716:Replication Protein A; D004247:DNA