Butler Margaret I, Gray Jeremy, Goodwin Timothy J D, Poulter Russell T M
Department of Biochemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand.
BMC Evol Biol. 2006 May 31;6:42. doi: 10.1186/1471-2148-6-42.
We recently described a mini-intein in the PRP8 gene of a strain of the basidiomycete Cryptococcus neoformans, an important fungal pathogen of humans. This was the second described intein in the nuclear genome of any eukaryote; the first nuclear encoded intein was found in the VMA gene of several saccharomycete yeasts. The evolution of eukaryote inteins is not well understood. In this report we describe additional PRP8 inteins (bringing the total of these to over 20). We compare and contrast the phylogenetic distribution and evolutionary history of the PRP8 intein and the saccharomycete VMA intein, in order to derive a broader understanding of eukaryote intein evolution. It has been suggested that eukaryote inteins undergo horizontal transfer and the present analysis explores this proposal.
In total, 22 PRP8 inteins have been detected in species from three different orders of euascomycetes, including Aspergillus nidulans and Aspergillus fumigatus (Eurotiales), Paracoccidiodes brasiliensis, Uncinocarpus reesii and Histoplasma capsulatum (Onygales) and Botrytis cinerea (Helotiales). These inteins are all at the same site in the PRP8 sequence as the original Cryptococcus neoformans intein. Some of the PRP8 inteins contain apparently intact homing endonuclease domains and are thus potentially mobile, while some lack the region corresponding to the homing endonuclease and are thus mini-inteins. In contrast, no mini-inteins have been reported in the VMA gene of yeast. There are several examples of pairs of closely related species where one species carries the PRP8 intein while the intein is absent from the other species. Bio-informatic and phylogenetic analyses suggest that many of the ascomycete PRP8 homing endonucleases are active. This contrasts with the VMA homing endonucleases, most of which are inactive.
PRP8 inteins are widespread in the euascomycetes (Pezizomycota) and apparently their homing endonucleases are active. There is no evidence for horizontal transfer within the euascomycetes. This suggests that the intein is of ancient origin and has been vertically transmitted amongst the euascomycetes. It is possible that horizontal transfer has occurred between the euascomycetes and members of the basidiomycete genus Cryptococcus.
我们最近在担子菌新生隐球菌的一个菌株的PRP8基因中描述了一种小内含肽，新生隐球菌是人类重要的真菌病原体。这是在任何真核生物核基因组中发现的第二个内含肽；第一个核编码内含肽是在几种酿酒酵母的VMA基因中发现的。真核生物内含肽的进化尚未得到很好的理解。在本报告中，我们描述了更多的PRP8内含肽（总数超过20个）。我们比较并对比了PRP8内含肽和酿酒酵母VMA内含肽的系统发育分布和进化历史，以便更广泛地理解真核生物内含肽的进化。有人提出真核生物内含肽会发生水平转移，本分析探讨了这一观点。
总共在来自三个不同目子囊菌的物种中检测到22个PRP8内含肽，包括构巢曲霉和烟曲霉（散囊菌目）、巴西副球孢子菌、里斯被孢霉和荚膜组织胞浆菌（爪甲团囊菌目）以及灰葡萄孢（柔膜菌目）。这些内含肽在PRP8序列中的位置与原始新生隐球菌内含肽相同。一些PRP8内含肽含有明显完整的归巢内切酶结构域并因此可能具有移动性，而一些则缺少与归巢内切酶对应的区域，因此是小内含肽。相比之下，酵母的VMA基因中尚未报道过小内含肽。有几个密切相关物种对的例子，其中一个物种携带PRP8内含肽而另一个物种没有。生物信息学和系统发育分析表明，许多子囊菌PRP8归巢内切酶是有活性的。这与VMA归巢内切酶形成对比，其中大多数是无活性的。
PRP8内含肽在子囊菌（盘菌门）中广泛存在，显然它们的归巢内切酶是有活性的。没有证据表明在子囊菌内部发生水平转移。这表明该内含肽起源古老，并且在子囊菌之间垂直传递。有可能在子囊菌和担子菌新生隐球菌属成员之间发生了水平转移。
