Dna2 nuclease resolves RNA:DNA hybrids at double-strand breaks

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• DNA double-strand breaks (DSBs) are critical DNA lesions requiring precise repair to prevent genomic instability.
• RNA:DNA hybrids (RDHs) transiently form during DSB repair, and their timely resolution is essential for accurate repair pathways.
• The precise roles of nucleases, such as Dna2, in resolving RDHs at DSBs are not fully understood.

Purpose of the Study:

• To investigate the role of the Dna2 nuclease in the resolution of RNA:DNA hybrids (RDHs) at DNA double-strand breaks (DSBs).
• To determine how Dna2 activity influences RDH accumulation and subsequent DNA repair processes.
• To elucidate the substrate specificity of Dna2 in resolving RDHs compared to other nucleases like Exo1.

Main Methods:

• Utilized genetic manipulation to alter Dna2 activity and Nej1 presence at DSBs.
• Quantified RDH levels in various mutant backgrounds, including Dna2 nuclease-dead mutants and RNH201 deletions.
• Assessed the substrate preference of Dna2 for RDHs versus DNA duplexes in vitro.

Main Results:

• Absence of the end-joining factor Nej1 at DSBs led to reduced RDH levels and increased Dna2 nuclease activity.
• Dna2 was found to limit RDH accumulation at DSBs, with higher levels observed in nuclease-dead Dna2 mutants and RNH201 deletions.
• Dna2 demonstrated a preference for resolving RDHs with 5' RNA overhangs over DNA duplexes with 5' DNA overhangs.
• This selective resolution by Dna2 promotes DNA resection, a function distinct from Exo1.

Conclusions:

• Dna2 plays a crucial role in resolving RDHs at DSBs, thereby preventing the accumulation of potentially harmful nucleic acid structures.
• Dna2's ability to resolve RDHs contributes to efficient DNA resection and homology-directed repair.
• This study highlights the multifunctional nature of Dna2 as a key player in maintaining genome integrity during DSB repair.