Department of Molecular and Cell Biology, University of California, Merced, Merced, CA 95343, USA.
Department of Biology and Ecology Faculty of Science, University of Ostrava, Ostrava, Czech Republic.
Curr Biol. 2021 Jul 26;31(14):3125-3131.e4. doi: 10.1016/j.cub.2021.04.050. Epub 2021 May 19.
Spliceosomal introns interrupt nuclear genes and are removed from RNA transcripts ("spliced") by machinery called spliceosomes. Although the vast majority of spliceosomal introns are removed by the so-called major (or "U2") spliceosome, diverse eukaryotes also contain a rare second form, the minor ("U12") spliceosome, and associated ("U12-type") introns. In all characterized species, U12-type introns are distinguished by several features, including being rare in the genome (∼0.5% of all introns), containing extended evolutionarily conserved splicing motifs, being generally ancient, and being inefficiently spliced. Here, we report a remarkable exception in the slime mold Physarum polycephalum. The P. polycephalum genome contains >20,000 U12-type introns-25 times more than any other species-enriched in a diversity of non-canonical splice boundaries as well as transformed splicing signals that appear to have co-evolved with the spliceosome due to massive gain of efficiently spliced U12-type introns. These results reveal an unappreciated dynamism of minor spliceosomal introns and spliceosomal introns in general.
剪接体内含子打断核基因，并通过称为剪接体的机制从 RNA 转录本中被去除（“剪接”）。尽管绝大多数剪接体内含子是由所谓的主要（或“U2”）剪接体去除的，但多样化的真核生物也含有罕见的第二种形式，即次要（“U12”）剪接体和相关的（“U12 型”）内含子。在所有已鉴定的物种中，U12 型内含子具有几个特征，包括在基因组中很少见（∼0.5%的内含子），含有扩展的进化保守的剪接基序，通常是古老的，并且剪接效率低下。在这里，我们在粘菌 Physarum polycephalum 中报告了一个显著的例外。P. polycephalum 基因组包含超过 20,000 个 U12 型内含子——比任何其他物种都多 25 倍——富含各种非规范的剪接边界以及转化的剪接信号，这些信号似乎由于大量高效剪接的 U12 型内含子的获得而与剪接体共同进化。这些结果揭示了次要剪接体内含子和一般剪接体内含子的一种未被认识到的动态性。
