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Pso2 (SNM1) is a DNA structure-specific endonuclease.

Tiefenbach T, Junop M - Nucleic Acids Res. (2011)

Bottom Line: Here we present biochemical and genetic evidence to suggest that Pso2 is a robust DNA hairpin opening nuclease in budding yeast.In this study, we characterized the nuclease activity of Pso2 toward a variety of DNA substrates.Unexpectedly, Pso2 was found to be an efficient, structure-specific DNA hairpin opening endonuclease.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario L8N 3Z5, Canada.

ABSTRACT
Many types of DNA structures are generated in response to DNA damage, repair and recombination that require processing via specialized nucleases. DNA hairpins represent one such class of structures formed during V(D)J recombination, palindrome extrusion, DNA transposition and some types of double-strand breaks. Here we present biochemical and genetic evidence to suggest that Pso2 is a robust DNA hairpin opening nuclease in budding yeast. Pso2 (SNM1A in mammals) belongs to a small group of proteins thought to function predominantly during interstrand crosslink (ICL) repair. In this study, we characterized the nuclease activity of Pso2 toward a variety of DNA substrates. Unexpectedly, Pso2 was found to be an efficient, structure-specific DNA hairpin opening endonuclease. This activity was further shown to be required in vivo for repair of chromosomal breaks harboring closed hairpin ends. These findings provide the first evidence that Pso2 may function outside ICL repair and open the possibility that Pso2 may function at least in part during ICL repair by processing DNA intermediates including DNA hairpins or hairpin-like structures.

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Related in: MedlinePlus

Model for generation and repair of hairpins during ICL damage. As the replication fork moves toward an ICL lesion helicase causes cruciform extrusion between the fork and ICL. Topoisomerase I activity ahead of the ICL also may create cruciform structures. Cruciform structures are resolved into hairpin capped DSBs (3, Cote and Lewis, 2008). Pso2 and/or the MRX/Sae2 complex process hairpin structures for subsequent end-joining repair.
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gkr1059-F5: Model for generation and repair of hairpins during ICL damage. As the replication fork moves toward an ICL lesion helicase causes cruciform extrusion between the fork and ICL. Topoisomerase I activity ahead of the ICL also may create cruciform structures. Cruciform structures are resolved into hairpin capped DSBs (3, Cote and Lewis, 2008). Pso2 and/or the MRX/Sae2 complex process hairpin structures for subsequent end-joining repair.

Mentions: How might DNA hairpins be generated during ICL damage and/or repair? Several possibilities exist. Introduction of a DNA interstrand crosslink creates a physical barrier to DNA replication, causing stalling, fork collapse and formation of DSBs (45). In support of this idea, DSBs are found to accumulate to a greater extent in actively versus non-actively replicating cells following exposure to ICL-inducing agents (46). Brendel et al. (22) proposed a model whereby movement of the replication fork toward an ICL lesion would cause cruciform extrusion (Figure 5). These structures could be generated on both sides of an ICL lesion due to topoisomerase I activity functioning ahead of the replication fork. Similar to cruciforms formed at long inverted repeats in yeast (3), cruciforms generated by replication toward an ICL would be converted into various sized hairpin-capped double stranded breaks (Figure 5) (10). These substrates may in turn serve as intermediates for MRX and/or Pso2 endonuclease activities. Consistent with this hypothesis, deletion of PSO2 has been shown to result in accumulation of DSBs (26). As such, it is thought that Pso2 functions subsequent to DSB formation in ICL repair. The biochemical and genetic analysis of Pso2 presented here, is consistent with at least a subset of these DSBs being capped by hairpin structures.Figure 5.


Pso2 (SNM1) is a DNA structure-specific endonuclease.

Tiefenbach T, Junop M - Nucleic Acids Res. (2011)

Model for generation and repair of hairpins during ICL damage. As the replication fork moves toward an ICL lesion helicase causes cruciform extrusion between the fork and ICL. Topoisomerase I activity ahead of the ICL also may create cruciform structures. Cruciform structures are resolved into hairpin capped DSBs (3, Cote and Lewis, 2008). Pso2 and/or the MRX/Sae2 complex process hairpin structures for subsequent end-joining repair.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3299998&req=5

gkr1059-F5: Model for generation and repair of hairpins during ICL damage. As the replication fork moves toward an ICL lesion helicase causes cruciform extrusion between the fork and ICL. Topoisomerase I activity ahead of the ICL also may create cruciform structures. Cruciform structures are resolved into hairpin capped DSBs (3, Cote and Lewis, 2008). Pso2 and/or the MRX/Sae2 complex process hairpin structures for subsequent end-joining repair.
Mentions: How might DNA hairpins be generated during ICL damage and/or repair? Several possibilities exist. Introduction of a DNA interstrand crosslink creates a physical barrier to DNA replication, causing stalling, fork collapse and formation of DSBs (45). In support of this idea, DSBs are found to accumulate to a greater extent in actively versus non-actively replicating cells following exposure to ICL-inducing agents (46). Brendel et al. (22) proposed a model whereby movement of the replication fork toward an ICL lesion would cause cruciform extrusion (Figure 5). These structures could be generated on both sides of an ICL lesion due to topoisomerase I activity functioning ahead of the replication fork. Similar to cruciforms formed at long inverted repeats in yeast (3), cruciforms generated by replication toward an ICL would be converted into various sized hairpin-capped double stranded breaks (Figure 5) (10). These substrates may in turn serve as intermediates for MRX and/or Pso2 endonuclease activities. Consistent with this hypothesis, deletion of PSO2 has been shown to result in accumulation of DSBs (26). As such, it is thought that Pso2 functions subsequent to DSB formation in ICL repair. The biochemical and genetic analysis of Pso2 presented here, is consistent with at least a subset of these DSBs being capped by hairpin structures.Figure 5.

Bottom Line: Here we present biochemical and genetic evidence to suggest that Pso2 is a robust DNA hairpin opening nuclease in budding yeast.In this study, we characterized the nuclease activity of Pso2 toward a variety of DNA substrates.Unexpectedly, Pso2 was found to be an efficient, structure-specific DNA hairpin opening endonuclease.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario L8N 3Z5, Canada.

ABSTRACT
Many types of DNA structures are generated in response to DNA damage, repair and recombination that require processing via specialized nucleases. DNA hairpins represent one such class of structures formed during V(D)J recombination, palindrome extrusion, DNA transposition and some types of double-strand breaks. Here we present biochemical and genetic evidence to suggest that Pso2 is a robust DNA hairpin opening nuclease in budding yeast. Pso2 (SNM1A in mammals) belongs to a small group of proteins thought to function predominantly during interstrand crosslink (ICL) repair. In this study, we characterized the nuclease activity of Pso2 toward a variety of DNA substrates. Unexpectedly, Pso2 was found to be an efficient, structure-specific DNA hairpin opening endonuclease. This activity was further shown to be required in vivo for repair of chromosomal breaks harboring closed hairpin ends. These findings provide the first evidence that Pso2 may function outside ICL repair and open the possibility that Pso2 may function at least in part during ICL repair by processing DNA intermediates including DNA hairpins or hairpin-like structures.

Show MeSH
Related in: MedlinePlus