Fekete Erzsébet, Flipphi Michel, Ág Norbert, Kavalecz Napsugár, Cerqueira Gustavo, Scazzocchio Claudio, Karaffa Levente
Department of Biochemical Engineering, University of Debrecen, 4032, Hungary.
Broad Institute of MIT & Harvard, Cambridge, 02141 MA, USA.
Nucleic Acids Res. 2017 Sep 6;45(15):9085-9092. doi: 10.1093/nar/gkx520.
Spliceosomal introns can occupy nearby rather than identical positions in orthologous genes (intron sliding or shifting). Stwintrons are complex intervening sequences, where an 'internal' intron interrupts one of the sequences essential for splicing, generating after its excision, a newly formed canonical intron defined as 'external'. In one experimentally demonstrated configuration, two alternatively excised internal introns, overlapping by one G, disrupt respectively the donor and the acceptor sequence of an external intron, leading to mRNAs encoding identical proteins. In a gene encoding a DHA1 antiporter in Pezizomycotina, we find a variety of predicted intron configurations interrupting the DNA stretch encoding a conserved peptidic sequence. Some sport a stwintron where the internal intron interrupts the donor of the external intron (experimentally confirmed for Aspergillus nidulans). In others, we found and demonstrate (for Trichoderma reesei) alternative, overlapping internal introns. Discordant canonical introns, one nt apart, are present in yet other species, exactly as predicted by the alternative loss of either of the internal introns at the DNA level from an alternatively spliced stwintron. An evolutionary pathway of 1 nt intron shift, involving an alternatively spliced stwintron intermediate is proposed on the basis of the experimental and genomic data presented.
剪接体内含子在直系同源基因中可占据相近而非相同的位置（内含子滑动或移位）。双内含子是复杂的居间序列，其中一个“内部”内含子打断剪接所需的序列之一，切除后会产生一个新形成的被定义为“外部”的典型内含子。在一种经实验证实的结构中，两个可选择性切除的内部内含子，有一个G重叠，分别破坏一个外部内含子的供体和受体序列，导致编码相同蛋白质的mRNA。在一个编码盘菌亚门中DHA1反向转运蛋白的基因中，我们发现多种预测的内含子结构打断了编码保守肽序列的DNA片段。有些带有双内含子，其中内部内含子打断外部内含子的供体（构巢曲霉已通过实验证实）。在其他物种中，我们发现并证明（里氏木霉）存在可选择性的、重叠的内部内含子。在其他物种中还存在相差一个核苷酸的不一致的典型内含子，正如从一个可变剪接的双内含子在DNA水平上内部内含子之一的选择性缺失所预测的那样。基于所呈现的实验和基因组数据，提出了一种涉及可变剪接双内含子中间体的1个核苷酸内含子移位的进化途径。
