Human base excision repair creates a bias toward -1 frameshift mutations

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Frameshift mutations are critical in cancer development, often arising from DNA polymerase slippage.
• The mismatch repair pathway corrects polymerase errors, but base excision repair (BER) pathway enzymes can increase frameshift mutation frequency.

Purpose of the Study:

• To investigate the role of the base excision repair (BER) pathway in processing DNA with single nucleotide bulges.
• To understand how BER activity influences frameshift mutation outcomes, particularly the deletion bias.

Main Methods:

• Analysis of DNA containing single nucleotide bulges in human cell extracts.
• Characterization of nucleotide removal and adduct formation using purified BER components.
• Modeling the impact of bulged DNA processing on frameshift events.

Main Results:

• Human cell extracts efficiently remove deaminated or alkylated nucleotides from single nucleotide bulges via BER.
• Chloroacetaldehyde reacts significantly faster with bulged adenine than with a standard base pair, forming adducts processed by alkyladenine DNA glycosylase.
• Purified BER components effectively process bulged DNA.

Conclusions:

• The base excision repair (BER) pathway actively processes DNA with single nucleotide bulges.
• BER's processing of bulged DNA may contribute to the observed bias towards deletion mutations in frameshift events.