Di Giulio Massimo
Laboratory for Molecular Evolution, Institute of Genetics and Biophysics Adriano Buzzati Traverso, CNR, Via P. Castellino, 111, 80131 Naples, Napoli, Italy.
Gene. 2008 Sep 15;421(1-2):20-6. doi: 10.1016/j.gene.2008.06.010. Epub 2008 Jun 11.
The introns early hypothesis predicts that introns were fundamental in assembling the first genes. In Nanoarchaeum equitans some genes are split into two. If these split genes were the ancestral forms, as suggested by the introns early hypothesis, then the end-beginning of the two parts of the split protein in a multiple alignment with the orthologous proteins from the Eukarya and Arachaea domains should make a clear prediction on where the intron in the homologous eukaryotic gene should be positioned. The analysis has shown that the introns are in this position, which is therefore predictable on the basis of the split proteins of N. equitans. This corroborates the hypothesis that the split genes of N. equitans are the plesiomorphic forms of these genes. If true, this would show that the origin of genes was polyphyletic as the monophyletic origin hypothesis would deny the existence, in a real organism, of these ancestral (split) genes, which imply that they were assembled late on and after the domains of life were established. Furthermore, it would seem that hyperthermophily is also an ancestral trait because it is linked to a split gene in N. equitans.
内含子早期假说预测，内含子在组装首批基因的过程中起着基础性作用。在嗜热栖热菌中，有些基因被分割成两部分。如果按照内含子早期假说所暗示的那样，这些分割基因是祖先形式，那么在与真核生物域和古菌域的直系同源蛋白质进行多重比对时，分割蛋白质两部分的首尾应该能对同源真核基因中的内含子位置做出明确预测。分析表明，内含子就在这个位置，因此基于嗜热栖热菌的分割蛋白质可以预测到这一点。这证实了嗜热栖热菌的分割基因是这些基因的近祖形式这一假说。如果这是真的，那就表明基因的起源是多系的，因为单系起源假说会否认在真实生物体中存在这些祖先（分割）基因，这意味着它们是在生命域建立之后才后期组装而成的。此外，嗜热似乎也是一种祖先特征，因为它与嗜热栖热菌中的一个分割基因有关。
