Biochemistry Department, University of Otago, Dunedin 9054, New Zealand.
Fungal Genet Biol. 2012 Mar;49(3):250-61. doi: 10.1016/j.fgb.2012.01.001. Epub 2012 Jan 20.
The mobile elements termed inteins have a sporadic distribution in microorganisms. It is unclear how these elements are maintained. Inteins are intervening protein sequences that autocatalytically excise themselves from a precursor. Excision is a post-translational process referred to as 'protein splicing' in which the sequences flanking the intein are ligated, reforming the mature host protein. Some inteins contain a homing endonuclease domain (HEG) that is proposed to facilitate propagation of the intein element within a gene pool. We have previously demonstrated that the HEG of the PRP8 intein is highly active during meiosis in Botrytis cinerea. Here we analysed the Prp8 gene status in 21 additional Botrytis species to obtain insight into the mode of intein inheritance within the Botrytis lineage. Of the 21 species, 15 contained a PRP8 intein whereas six did not. The analysis was extended to closely related (Sclerotiniaceae) and distantly related (Ascomycota) taxa, focussing on evolutionary diversification of the PRP8 intein, including their possible acquisition by horizontal transfer and loss by deletion. Evidence was obtained for the occurrence of genetic footprints of previous intein occupation. There is no compelling evidence of horizontal transfer among species. Three distinct states of the Prp8 allele were identified, distributed over different orders within the Ascomycota: an occupied allele; an empty allele that was never occupied; an empty allele that was presumably previously occupied, from which the intein was precisely deleted. The presence of the genetic footprint identifies 20 species (including Neurospora crassa, Magnaporthe oryzae and Fusarium oxysporum) that previously contained the intein but have lost it entirely, while only 18 species (including Podospora anserina and Fusarium graminearum) appear never to have contained a PRP8 intein. The analysis indicates that inteins may be maintained in an equilibrium state.
移动元件称为内含子，在微生物中有散在分布。这些元件如何被维持尚不清楚。内含子是自行从前体中切除的插入蛋白序列。切除是一种翻译后过程，在该过程中，内含子侧翼的序列被连接，重新形成成熟的宿主蛋白。一些内含子含有一个同源内切酶结构域（HEG），据推测该结构域有助于内含子元件在基因库内的传播。我们之前已经证明，葡萄孢菌 PRP8 内含子的 HEG 在减数分裂过程中高度活跃。在这里，我们分析了 21 种额外的 Botrytis 物种中的 Prp8 基因状态，以深入了解内含子在 Botrytis 谱系内的遗传模式。在 21 个物种中，有 15 个含有 PRP8 内含子，而有 6 个没有。分析扩展到了密切相关的（核盘菌科）和远缘相关的（子囊菌门）分类群，重点研究 PRP8 内含子的进化多样化，包括它们可能通过水平转移获得和通过缺失丢失。获得了内含子先前占据的遗传足迹发生的证据。没有令人信服的证据表明物种间存在水平转移。鉴定出 Prp8 等位基因的三种不同状态，分布在子囊菌门的不同阶元中：一个被占据的等位基因；一个从未被占据的空等位基因；一个空等位基因，据推测之前被占据，内含子被精确删除。遗传足迹的存在确定了 20 个物种（包括粗糙脉孢菌、稻瘟病菌和尖孢镰刀菌）之前含有内含子但已完全丢失，而只有 18 个物种（包括构巢曲霉和禾谷镰刀菌）似乎从未含有 PRP8 内含子。该分析表明，内含子可能处于平衡状态。
