The Werner syndrome helicase/exonuclease processes mobile D-loops through branch migration and degradation.

RecQ DNA helicases are critical for preserving genome integrity. Of the five RecQ family members identified in humans, only the Werner syndrome protein (WRN) possesses exonuclease activity. Loss of WRN causes the progeroid disorder Werner syndrome which is marked by cancer predisposition. Cellular e...

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Main Authors: Patricia L Opresko, Gregory Sowd, Hong Wang
Format: Article
Language:English
Published: Public Library of Science (PLoS) 2009-01-01
Series:PLoS ONE
Online Access:http://europepmc.org/articles/PMC2653227?pdf=render
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spelling doaj-2d485540115f4c90ac1b5bcd4632cced2020-11-24T22:06:49ZengPublic Library of Science (PLoS)PLoS ONE1932-62032009-01-0143e482510.1371/journal.pone.0004825The Werner syndrome helicase/exonuclease processes mobile D-loops through branch migration and degradation.Patricia L OpreskoGregory SowdHong WangRecQ DNA helicases are critical for preserving genome integrity. Of the five RecQ family members identified in humans, only the Werner syndrome protein (WRN) possesses exonuclease activity. Loss of WRN causes the progeroid disorder Werner syndrome which is marked by cancer predisposition. Cellular evidence indicates that WRN disrupts potentially deleterious intermediates in homologous recombination (HR) that arise in genomic and telomeric regions during DNA replication and repair. Precisely how the WRN biochemical activities process these structures is unknown, especially since the DNA unwinding activity is poorly processive. We generated biologically relevant mobile D-loops which mimic the initial DNA strand invasion step in HR to investigate whether WRN biochemical activities can disrupt this joint molecule. We show that WRN helicase alone can promote branch migration through an 84 base pair duplex region to completely displace the invading strand from the D-loop. However, substrate processing is altered in the presence of the WRN exonuclease activity which degrades the invading strand both prior to and after release from the D-loop. Furthermore, telomeric D-loops are more refractory to disruption by WRN, which has implications for tighter regulation of D-loop processing at telomeres. Finally, we show that WRN can recognize and initiate branch migration from both the 5' and 3' ends of the invading strand in the D-loops. These findings led us to propose a novel model for WRN D-loop disruption. Our biochemical results offer an explanation for the cellular studies that indicate both WRN activities function in processing HR intermediates.http://europepmc.org/articles/PMC2653227?pdf=render
collection DOAJ
language English
format Article
sources DOAJ
author Patricia L Opresko
Gregory Sowd
Hong Wang
spellingShingle Patricia L Opresko
Gregory Sowd
Hong Wang
The Werner syndrome helicase/exonuclease processes mobile D-loops through branch migration and degradation.
PLoS ONE
author_facet Patricia L Opresko
Gregory Sowd
Hong Wang
author_sort Patricia L Opresko
title The Werner syndrome helicase/exonuclease processes mobile D-loops through branch migration and degradation.
title_short The Werner syndrome helicase/exonuclease processes mobile D-loops through branch migration and degradation.
title_full The Werner syndrome helicase/exonuclease processes mobile D-loops through branch migration and degradation.
title_fullStr The Werner syndrome helicase/exonuclease processes mobile D-loops through branch migration and degradation.
title_full_unstemmed The Werner syndrome helicase/exonuclease processes mobile D-loops through branch migration and degradation.
title_sort werner syndrome helicase/exonuclease processes mobile d-loops through branch migration and degradation.
publisher Public Library of Science (PLoS)
series PLoS ONE
issn 1932-6203
publishDate 2009-01-01
description RecQ DNA helicases are critical for preserving genome integrity. Of the five RecQ family members identified in humans, only the Werner syndrome protein (WRN) possesses exonuclease activity. Loss of WRN causes the progeroid disorder Werner syndrome which is marked by cancer predisposition. Cellular evidence indicates that WRN disrupts potentially deleterious intermediates in homologous recombination (HR) that arise in genomic and telomeric regions during DNA replication and repair. Precisely how the WRN biochemical activities process these structures is unknown, especially since the DNA unwinding activity is poorly processive. We generated biologically relevant mobile D-loops which mimic the initial DNA strand invasion step in HR to investigate whether WRN biochemical activities can disrupt this joint molecule. We show that WRN helicase alone can promote branch migration through an 84 base pair duplex region to completely displace the invading strand from the D-loop. However, substrate processing is altered in the presence of the WRN exonuclease activity which degrades the invading strand both prior to and after release from the D-loop. Furthermore, telomeric D-loops are more refractory to disruption by WRN, which has implications for tighter regulation of D-loop processing at telomeres. Finally, we show that WRN can recognize and initiate branch migration from both the 5' and 3' ends of the invading strand in the D-loops. These findings led us to propose a novel model for WRN D-loop disruption. Our biochemical results offer an explanation for the cellular studies that indicate both WRN activities function in processing HR intermediates.
url http://europepmc.org/articles/PMC2653227?pdf=render
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