Inhibition of FEN-1 processing by DNA secondary structure at trinucleotide repeats

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• The precise mechanisms driving trinucleotide repeat expansions in human genes remain largely unknown.
• A hypothesis suggests that DNA secondary structures may impede the cleavage of Okazaki fragments by the flap endonuclease 1 (FEN-1).

Purpose of the Study:

• To investigate the role of DNA secondary structures in trinucleotide repeat expansion.
• To elucidate the involvement of FEN-1 in this process.

Main Methods:

• Experimental analysis of DNA secondary structure formation at repeat sequences.
• Assays to measure FEN-1 cleavage activity in the presence and absence of secondary structures.
• Studies on trinucleotide repeat expansion in cellular models with varying FEN-1 levels.

Main Results:

• DNA secondary structures were shown to inhibit FEN-1 cleavage of Okazaki fragments at CAG, CGG, and CTG repeats.
• This inhibition occurs in a length-dependent manner by masking the flap's 5' end, crucial for FEN-1 binding and cleavage.
• In FEN-1-deficient cells, alternative mechanisms contribute to repeat expansions beyond simple flap processing inhibition.

Conclusions:

• DNA secondary structures actively contribute to trinucleotide repeat expansions via a FEN-1-dependent pathway.
• FEN-1's protective function against expansion can be overcome by secondary structures.
• Understanding these mechanisms is vital for developing therapeutic strategies against genetic disorders caused by repeat expansions.