Origin of endogenous DNA abasic sites in Saccharomyces cerevisiae

Area of Science:

• DNA repair mechanisms
• Molecular biology
• Genetics

Background:

• Abasic (AP) sites are frequent endogenous DNA lesions that impede DNA replication.
• A triple mutant yeast strain (apn1 apn2 rad1) lacking key AP site repair pathways is inviable.
• The origin of endogenous AP sites in yeast requires further investigation.

Purpose of the Study:

• To identify the primary endogenous sources of abasic (AP) sites in Saccharomyces cerevisiae.
• To investigate the role of specific DNA glycosylases and dUTP metabolism in AP site formation.
• To understand the genetic basis for the inviability of AP site repair-deficient yeast mutants.

Main Methods:

• Genetic analysis of yeast mutants with deletions or overexpressions of DNA repair genes (UNG1, MAG1, OGG1, NTG1, NTG2, DUT1).
• Assessment of mutant strain viability and growth phenotypes.
• Investigation of the genetic interactions between AP site repair pathways and uracil metabolism.

Main Results:

• Deletion of the UNG1 gene (uracil DNA glycosylase) rescued the inviability of the apn1 apn2 rad1 mutant.
• Inactivation of other DNA glycosylases (MAG1, OGG1, NTG1, NTG2) did not rescue the mutant.
• Overexpression of DUT1 (dUTP pyrophosphatase) also suppressed the lethality, indicating the dUTP pool's significance.
• The apn1 apn2 rad1 ung1 mutant exhibited growth delay due to a G(2)/M checkpoint.

Conclusions:

• Uracil incorporation into DNA is a critical source of endogenous abasic (AP) sites in yeast.
• The dUTP pool, regulated by dUTP pyrophosphatase, significantly contributes to endogenous AP site formation.
• Targeting uracil excision and dUTP metabolism are potential strategies for managing AP sites in eukaryotes.