Abstract
We discuss three major processes that silence genes in filamentous fungi. Repeat-induced point mutation (RIP) causes permanent silencing of repeated genes inNeurospora crassa by peppering them with G:C to A:T mutations during the premeiotic stage of the sexual cycle. A related process, methylation induced premeiotically (MIP), operates during the sexual cycle inAscobolus immersus andCoprinus cinereus to reversibly silence repeated sequences by methylating them. Both processes appear to use a homologous pairing mechanism to sense the presence of duplications. Both MIP and RIP result in dense methylation of cytosines located in nonsymmetrical sequences. This methylation is either always (for MIP) or sometimes (for RIP) maintained during vegetative growth by a novel, epigenetic maintenance mechanism that is not well understood. The third silencing process, quelling inN. crassa, appears to involve post-transcriptional or cotranscriptional disruption of gene expression by transcripts produced from certain transgene loci. This form of silencing seems similar to silencing processes described in many plant species. Each of these genesilencing processes involves silencing of repeated sequences. Thus each is potentially useful for preventing proliferation of selfish DNA elements and for maintaining genome integrity by suppressing chromosomal rearrangements.
Published Version
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