Hypothesis: transcript-templated repair of DNA double-strand breaks.

Two mechanisms are available for the repair of DNA double-strand breaks (DSBs) in eukaryotic cells: homology directed repair (HDR) and non-homologous end-joining (NHEJ). While NHEJ is not restricted to a particular phase of the cell cycle, it is incapable of accurately repairing DBSs that have suffered a loss or gain of nucleotide sequence information. In contrast, HDR achieves accurate repair of such DSBs by use of a sister chromatid as a DNA template, but is restricted to cell cycle phases (S/G2) when such templates are available. In this scheme, G1 cells appear to lack a mechanism for the accurate repair of certain DSBs, and an ability to use alternative templates would be highly advantageous. Considered here, therefore, is the possibility that RNA transcripts are used as templates for HDR. Potential mechanisms for transcript-templated HDR, and ways in which it might be detected, are presented.