Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138.
Microbiol Spectr. 2017 Jul;5(4). doi: 10.1128/microbiolspec.FUNK-0042-2017.
Transposable elements have colonized the genomes of nearly all organisms, including fungi. Although transposable elements may sometimes provide beneficial functions to their hosts their overall impact is considered deleterious. As a result, the activity of transposable elements needs to be counterbalanced by the host genome defenses. In fungi, the primary genome defense mechanisms include repeat-induced point mutation (RIP) and methylation induced premeiotically, meiotic silencing by unpaired DNA, sex-induced silencing, cosuppression (also known as somatic quelling), and cotranscriptional RNA surveillance. Recent studies of the filamentous fungus have shown that the process of repeat recognition for RIP apparently involves interactions between coaligned double-stranded segments of chromosomal DNA. These studies have also shown that RIP can be mediated by the conserved pathway that establishes transcriptional (heterochromatic) silencing of repetitive DNA. In light of these new findings, RIP emerges as a specialized case of the general phenomenon of heterochromatic silencing of repetitive DNA.
转座元件已经在几乎所有生物体的基因组中定殖，包括真菌。虽然转座元件有时可能为其宿主提供有益的功能，但它们的总体影响被认为是有害的。因此，转座元件的活性需要被宿主基因组防御所平衡。在真菌中，主要的基因组防御机制包括重复诱导点突变（RIP）和甲基化诱导的减数前沉默、未配对 DNA 引起的减数沉默、性诱导沉默、共抑制（也称为体细胞沉默）和共转录 RNA 监测。最近对丝状真菌的研究表明，RIP 的重复识别过程显然涉及染色体 DNA 中双链段的共定位相互作用。这些研究还表明，RIP 可以由建立重复 DNA 转录（异染色质）沉默的保守途径介导。鉴于这些新发现，RIP 作为重复 DNA 异染色质沉默这一普遍现象的一个特殊情况出现了。
