Physical and functional mapping of the replication protein a interaction domain of the werner and bloom syndrome helicases.
The single-stranded DNA-binding protein replication protein A (RPA) interacts with several human RecQ DNA helicases that have important roles in maintaining genomic stability; however, the mechanism for RPA stimulation of DNA unwinding is not well understood. To map regions of Werner syndrome helicase (WRN) that interact with RPA, yeast two-hybrid studies, WRN affinity pull-down experiments and enzyme-linked immunosorbent assays with purified recombinant WRN protein fragments were performed. The results indicated that WRN has two RPA binding sites, a high affinity N-terminal site, and a lower affinity C-terminal site. Based on results from mapping studies, we sought to determine if the WRN N-terminal region harboring the high affinity RPA interaction site was important for RPA stimulation of WRN helicase activity. To accomplish this, we tested a catalytically active WRN helicase domain fragment (WRN(H-R)) that lacked the N-terminal RPA interaction site for its ability to unwind long DNA duplex substrates, which the wild-type enzyme can efficiently unwind only in the presence of RPA. WRN(H-R) helicase activity was significantly reduced on RPA-dependent partial duplex substrates compared with full-length WRN despite the presence of RPA. These results clearly demonstrate that, although WRN(H-R) had comparable helicase activity to full-length WRN on short duplex substrates, its ability to unwind RPA-dependent WRN helicase substrates was significantly impaired. Similarly, a Bloom syndrome helicase (BLM) domain fragment, BLM(642-1290), that lacked its N-terminal RPA interaction site also unwound short DNA duplex substrates similar to wild-type BLM, but was severely compromised in its ability to unwind long DNA substrates that full-length BLM helicase could unwind in the presence of RPA. These results suggest that the physical interaction between RPA and WRN or BLM helicases plays an important role in the mechanism for RPA stimulation of helicase-catalyzed DNA unwinding.
Doherty
Kevin M
KM
Laboratory of Molecular Gerontology, NIA, National Institutes of Health, Baltimore, Maryland 21224, USA.
Sommers
Joshua A
JA
Gray
Matthew D
MD
Lee
Jae Wan
JW
von Kobbe
Cayetano
C
Thoma
Nicolas H
NH
Kureekattil
Raichal P
RP
Kenny
Mark K
MK
Brosh
Robert M
RM
D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000502:physiology; D001665:Binding Sites; D004247:DNA / Q000737:chemistry; D004265:DNA Helicases / Q000737:chemistry* / Q000502:physiology; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000502:physiology; D005090:Exodeoxyribonucleases; D006801:Humans; D053484:RecQ Helicases; D051716:Replication Protein A; D020798:Two-Hybrid System Techniques; D000071657:Werner Syndrome Helicase; D029867:Xenopus Proteins / Q000502:physiology
D004268:DNA-Binding Proteins; C497167:RPA1 protein, human; D051716:Replication Protein A; D029867:Xenopus Proteins; D004247:DNA; D005090:Exodeoxyribonucleases; D000251:Adenosine Triphosphatases; C097151:Bloom syndrome protein; D004265:DNA Helicases; D053484:RecQ Helicases; C098785:WRN protein, human; D000071657:Werner Syndrome Helicase; C507159:WRN protein, Xenopus