Processing of matched and mismatched rNMPs in DNA by archaeal ribonucleotide excision repair

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Ribonucleoside monophosphates (rNMPs) are non-canonical nucleotides found in genomic DNA.
• Incorporation of rNMPs can occur as matched or mismatched bases, posing mutagenic risks.
• Ribonucleotide excision repair (RER), initiated by RNase H, evolved to counteract rNMP mutagenicity.

Purpose of the Study:

• To reconstitute and characterize matched and mismatched rNMP repair pathways in vitro using archaeal RER enzymes.
• To investigate the in vivo role of specific enzymes, such as PolD, in the RER process.

Main Methods:

• In vitro reconstitution of archaeal ribonucleotide excision repair (RER) pathways.
• Biochemical assays using purified archaeal RER enzymes to study DNA repair mechanisms.
• Analysis of genomic rNMP levels in RER-deficient and PolB-deficient archaeal cells.

Main Results:

• Two distinct RER pathways were identified: classical flap RER and a backup RER pathway with altered enzyme order (Fen1 and Pols).
• In vitro reconstitution supported the roles of Fen1 and Pols in different RER mechanisms.
• Data from RER-deficient cells and in vitro assays suggest an in vivo function for PolD in the RER pathway.

Conclusions:

• The study provides a detailed in vitro model for understanding how both matched and mismatched rNMPs are processed by RER.
• Identified two RER pathways, offering insights into the redundancy and adaptability of DNA repair mechanisms.
• Highlights the potential in vivo significance of PolD in maintaining genomic integrity by managing rNMP incorporation.