DNA polymerase zeta can efficiently replicate structures formed by AT/TA repeat sequences and prevent their deletion

Area of Science:

• Genetics
• Molecular Biology
• Genomics

Background:

• Long AT repeat tracts can form non-B DNA structures, stalling DNA replication and causing chromosomal breakage.
• Human common fragile sites (CFSs) are AT-rich genomic regions prone to breakage under replication stress.

Purpose of the Study:

• To investigate the role of DNA polymerases in preventing breakage at AT-rich repetitive elements found in human CFS FRA16D.
• To elucidate the mechanism by which DNA polymerase zeta (Pol ζ) resolves non-B DNA structures.

Main Methods:

• Utilized an in vivo yeast model system with AT-rich repetitive elements from human CFS FRA16D.
• Employed purified replicative holoenzymes in vitro to assess DNA polymerase activity on hairpin structures.
• Investigated the roles of DNA polymerase zeta (Pol ζ), eta, delta, Rev1, and proliferating cell nuclear antigen (PCNA).

Main Results:

• DNA polymerase zeta (Pol ζ) is essential for preventing breakage and deletions at hairpin and cruciform forming (AT/TA)n sequences.
• DNA polymerase epsilon is significantly inhibited by hairpin structures, while Pol ζ efficiently replicates these regions.
• Rev1 protein and PCNA lysine 164 are implicated in Pol ζ recruitment for preventing deletions at AT/TA repeats.

Conclusions:

• DNA polymerase zeta (Pol ζ) plays a novel role in replicating through AT-rich hairpins, crucial for genomic stability.
• Pol ζ is vital for rescuing stalled replication forks caused by DNA structures at common fragile sites.