DOI 10.1007/s00294-008-0185-yRESEARCH ARTICLE Repeat induced point mutation in two asexual fungi, Aspergillus niger and Penicillium chrysogenum

Abstract Repeat induced point mutation (RIP) is a gene silencing mechanism present in fungal genomes. During RIP, duplicated sequences are eYciently and irreversibly mutated by transitions from C:G to T:A. For the Wrst time, we have identiWed traces of RIP in transposable elements of Aspergillus niger and Penicillium chrysogenum, two bio-technologically relevant fungi. We found that RIP in P. chrysogenum has aVected a large set of sequences, which also contain other mutations. On the other hand, RIP in A. niger is limited to only few sequences, but literally all mutations are RIP-like. Surprisingly, RIP occurred only in transposon sequences that have disrupted open reading frames in A. niger, a phenomenon not yet reported for other fungi. In both fungal species, we identiWed two sequences with strong sequence similarity to Neurospora crassa RID. RID is a putative DNA methyltransferase and the only known enzyme involved in the RIP process. Our Wndings suggest that both A. niger and P. chrysogenum either had a sexual past or have a sexual potential. These Wndings have important implications for future strain development of these fungi