Incision-dependent and error-free repair of (CAG)(n)/(CTG)(n) hairpins in human cell extracts.
Expansion of CAG/CTG trinucleotide repeats is associated with certain familial neurological disorders, including Huntington's disease. Increasing evidence suggests that formation of a stable DNA hairpin within CAG/CTG repeats during DNA metabolism contributes to their expansion. However, the molecular mechanism(s) by which cells remove CAG/CTG hairpins remain unknown. Here we demonstrate that human cell extracts can catalyze error-free repair of CAG/CTG hairpins in a nick-directed manner. The repair system specifically targets CAG/CTG tracts for incisions in the nicked DNA strand, followed by DNA resynthesis using the continuous strand as a template, thereby ensuring CAG/CTG stability. Proliferating cell nuclear antigen (PCNA) is required for the incision step of the hairpin removal, which uses distinct endonuclease activities for individual CAG/CTG hairpins depending on their strand locations and/or secondary structures. We discuss the implications of these data for understanding the etiology of neurological diseases and trinucleotide repeat instability.
Hou
Caixia
C
Graduate Center for Toxicology and Markey Cancer Center, University of Kentucky College of Medicine, Lexington, Kentucky, USA.
Chan
Nelson L S
NL
Gu
Liya
L
Li
Guo-Min
GM
D001483:Base Sequence; D002457:Cell Extracts / Q000737:chemistry* / Q000494:pharmacology; D004247:DNA / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D004260:DNA Repair / Q000187:drug effects / Q000235:genetics*; D045585:Flap Endonucleases / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008957:Models, Genetic; D009690:Nucleic Acid Conformation; D015345:Oligonucleotide Probes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D019680:Trinucleotide Repeat Expansion / Q000235:genetics; D018911:Trinucleotide Repeats / Q000235:genetics*
D002457:Cell Extracts; D015345:Oligonucleotide Probes; D018809:Proliferating Cell Nuclear Antigen; D004247:DNA; D045585:Flap Endonucleases