Mattick J S
Centre for Molecular and Cellular Biology, University of Queensland, Brisbane, Australia.
Curr Opin Genet Dev. 1994 Dec;4(6):823-31. doi: 10.1016/0959-437x(94)90066-3.
The debate continues on the issue of whether nuclear introns were present in eukaryotic protein-coding genes from the beginning (introns-early) or invaded them later in evolution (introns-late). Recent studies concerning the location of introns with respect to gene and protein structure have been interpreted as providing strong support for both positions, but the weight of argument is clearly moving in favour of the latter. Consistent with this, there is now good evidence that introns can function as transposable elements, and that nuclear introns derived from self-splicing group II introns, which then evolved in partnership with the spliceosome. This was only made possible by the separation of transcription and translation. If introns did colonize eukaryotic genes after their divergence from prokaryotes, the original question as to the evolutionary forces that have seen these sequences flourish in the higher organisms, and their significance in eukaryotic biology, is again thrown open. I suggest that introns, once established in eukaryotic genomes, might have explored new genetic space and acquired functions which provided a positive pressure for their expansion. I further suggest that there are now two types of information produced by eukaryotic genes--mRNA and iRNA--and that this was a critical step in the development of multicellular organisms.
关于核内含子从一开始就存在于真核生物蛋白质编码基因中（内含子早期）还是在进化后期侵入这些基因（内含子晚期）的问题，争论仍在继续。最近有关内含子相对于基因和蛋白质结构位置的研究被解读为对这两种观点都提供了有力支持，但论据的重心显然正朝着支持后者的方向转移。与此一致的是，现在有充分证据表明内含子可作为转座元件发挥作用，并且核内含子源自自我剪接的II类内含子，随后与剪接体协同进化。这只有通过转录和翻译的分离才成为可能。如果内含子确实是在真核生物与原核生物分化之后侵入真核基因的，那么关于促使这些序列在高等生物中大量存在的进化力量以及它们在真核生物学中的意义这一最初问题，就再次被提了出来。我认为，内含子一旦在真核基因组中确立，可能就探索了新的遗传空间并获得了功能，这些功能为其扩张提供了正向压力。我进一步认为，现在真核基因产生两种类型的信息——信使核糖核酸（mRNA）和干扰核糖核酸（iRNA），而这是多细胞生物发育中的关键一步。
