Jo Bong-Seok, Choi Sun Shim
Department of Medical Biotechnology, College of Biomedical Science, and Institute of Bioscience & Biotechnology, Kangwon National University, Chuncheon 24341, Korea.
Genomics Inform. 2015 Dec;13(4):112-8. doi: 10.5808/GI.2015.13.4.112. Epub 2015 Dec 31.
The intron has been a big biological mystery since it was first discovered in several aspects. First, all of the completely sequenced eukaryotes harbor introns in the genomic structure, whereas no prokaryotes identified so far carry introns. Second, the amount of total introns varies in different species. Third, the length and number of introns vary in different genes, even within the same species genome. Fourth, all introns are copied into RNAs by transcription and DNAs by replication processes, but intron sequences do not participate in protein-coding sequences. The existence of introns in the genome should be a burden to some cells, because cells have to consume a great deal of energy to copy and excise them exactly at the correct positions with the help of complicated spliceosomal machineries. The existence throughout the long evolutionary history is explained, only if selective advantages of carrying introns are assumed to be given to cells to overcome the negative effect of introns. In that regard, we summarize previous research about the functional roles or benefits of introns. Additionally, several other studies strongly suggesting that introns should not be junk will be introduced.
自首次被发现以来，内含子在多个方面一直是一个重大的生物学谜团。首先，所有已完成全基因组测序的真核生物在基因组结构中都含有内含子，而迄今为止所鉴定的原核生物都不携带内含子。其次，不同物种中内含子的总量各不相同。第三，即使在同一物种的基因组内，不同基因的内含子长度和数量也存在差异。第四，所有内含子在转录过程中被复制到RNA中，在复制过程中被复制到DNA中，但内含子序列并不参与蛋白质编码序列。基因组中内含子的存在对某些细胞来说应该是一种负担，因为细胞必须消耗大量能量，借助复杂的剪接体机制在正确位置精确复制和切除它们。只有假设携带内含子会给细胞带来选择性优势，以克服内含子的负面影响，才能解释其在漫长进化历史中的存在。在这方面，我们总结了先前关于内含子功能作用或益处的研究。此外，还将介绍其他几项有力表明内含子不应被视为垃圾的研究。
