Genome quality control: RIP (repeat-induced point mutation) comes to Podospora

RIP (repeat-induced point mutation) is a silencing process discovered in Ne urospora crassa and so far clearly established only in this species as a cu rrently occurring process. RIP acts premeiotically on duplicated sequences, resulting in C-G to T-A mutations, with a striking preference for CpA/TpG dinucleotides. In Podospora anserina, an RIP-like event was observed after several rounds of sexual reproduction in a strain with a 40 kb tandem dupli cation resulting from homologous integration of a cosmid in the mating-type region. The 9 kb sequenced show 106 C-G to T-A transitions, with 80% of th e replaced cytosines located in CpA dinucleotides. This led to the alterati on of at least six genes, two of which were unidentified. This RIP-like eve nt extended to single-copy genes between the two members of the repeat. The overall data show that the silencing process is strikingly similar to a li ght form of RIP, unaccompanied by C-methylation. Interestingly, the N. cras sa zeta-eta sequence, which acts as a potent de novo C-methylation RIP sign al in this species, is weakly methylated when introduced into P. anserina. These results demonstrate that RIP, at least in light forms, can occur beyo nd N. crassa.