Widespread occurrence of spliceosomal introns in the rDNA genes of ascomycetes
Widespread occurrence of spliceosomal introns in the rDNA genes of ascomycetes
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DOI：
10.1093/oxfordjournals.molbev.a026298
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发表时间：
2000-12-01
影响因子：
10.7
通讯作者：
Fernandez, F
中科院分区：
文献类型：
--
作者：
Bhattacharya, D;Lutzoni, F;Fernandez, F
剪接体（前mRNA）内含子先前已被发现在真核蛋白质编码基因，在一些真菌的小核RNA，并在小和大亚基核糖体DNA基因的数量有限的子囊菌。大多数内含子的起源仍然是一个悬而未决的问题，因为很少有证据证明最近和普遍的内含子起源的情况。我们在这里报告广泛发生的剪接体内含子（69内含子在27个不同的网站）在小和大亚基核编码的rDNA地衣形成和自由生活的子囊菌门的成员。我们的分析表明，这些剪接体内含子是相对较新的起源，即，在真子囊菌纲中，通过将游离前mRNA内含子异常反向剪接成rRNA而产生。剪接体本身，而不是外部媒介（例如，转座因子，第II组内含子），可能产生了这些内含子。一个非随机序列模式被发现在rRNA剪接体内含子两侧的网站。这种模式（AG-内含子-G）非常类似于前mRNA基因中内含子插入的原剪接位点（MAG-内含子-R）。剪接体内含子在二级结构上的聚集位置表明特定的rRNA区域是通过反向剪接插入的优选位点。
Spliceosomal (pre-mRNA) introns have previously been found in eukaryotic protein-coding genes, in the small nuclear RNAs of some fungi, and in the small- and large-subunit ribosomal DNA genes of a limited number of ascomycetes. How the majority of these introns originate remains an open question because few proven cases of recent and pervasive intron origin have been documented. We report here the widespread occurrence of spliceosomal introns (69 introns at 27 different sites) in the small- and large-subunit nuclear-encoded rDNA of lichen-forming and free-living members of the Ascomycota. Our analyses suggest that these spliceosomal introns are of relatively recent origin, i.e., within the Euascomycetes, and have arisen through aberrant reverse-splicing tin trans) of free pre-mRNA introns into rRNAs. The spliceosome itself, and not an external agent (e.g., transposable elements, group II introns), may have given rise to these introns. A nonrandom sequence pattern was found at sites flanking the rRNA spliceosomal introns. This pattern (AG-intron-G) closely resembles the proto-splice site (MAG-intron-R) postulated for intron insertions in pre-mRNA genes. The clustered positions of spliceosomal introns on secondary structures suggest that particular rRNA regions are preferred sites for insertion through reverse-splicing.