R loops stimulate genetic instability of CTG·CAG repeats

摘要: Transcription stimulates the genetic instability of trinucleotide repeat sequences. However, mechanisms leading to transcription-dependent length variation are unclear. We demonstrate, using biochemical and approaches, that formation stable RNA·DNA hybrids enhances CTG·CAG tracts. In vitro transcribed CG-rich repeating sequences, unlike AT-rich repeats nonrepeating form stable, ribonuclease A-resistant structures. These eliminated by H treatment. Mutation in rnhA1 gene decreases activity HI E. coli. Importantly, effect depletion on requires active transcription. also showed human cells is stimulated siRNA knockdown RNase H1 H2. In addition, we used bisulfite modification, which detects single-stranded DNA, demonstrate nontemplate DNA strand at remains partially genomic thus indicating it displaced an hybrid. studies persistent between nascent RNA transcript template tracts promote repeats.