question: Which DNA sequences are more prone for the formation of R-loops?
answer: R-loops, transcriptionally-induced RNA:DNA hybrids, occurring at repeat tracts (CTG)n, (CAG)n, (CGG)n, (CCG)n and (GAA)n, are associated with diseases including myotonic dystrophy, Huntington's disease, fragile X and Friedreich's ataxia.  Physiological R-loop formation at CpG island promoters can contribute to DNA replication origin specification at these regions, the most efficient replication initiation sites in mammalian cells. R-loops may also possess beneficial effects, as their widespread formation has been detected over CpG island promoters in human genes. R-loops are particularly enriched over G-rich terminator elements.