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It has been long debated whether spliceosomal introns originated in the common ancestor of eukaryotes and prokaryotes. In this study, we tested the possibility that extant introns were inherited from the common ancestor of eukaryotes and prokaryotes using in silico simulation. We first identified 21 intron positions that are shared among different families of the P-Type ATPase superfamily, some of which are known to have diverged before the separation of prokaryotes and eukaryotes. Theoretical estimates of the expected number of intron positions shared by different genes suggest that the introns at those 21 positions were inserted independently. There seems to be no intron that arose from before the diversification of the P-Type ATPase superfamily. Namely, the present introns were inserted after the separation of eukaryotes and prokaryotes. [ABSTRACT FROM AUTHOR]

Abstract: It was recently shown that there is a predominance of phase 1 introns near the cleavage site of signal peptides encoded by human genes [Tordai, H. and Patthy, L. (2004) Insertion of spliceosomal introns in proto-splice sites: the case of secretory signal peptides. FEBS Lett. 575, 109–111]. It was suggested that this biased distribution was due to intron insertion at AG∣G proto-splice sites. However, we found that there is no disproportional excess of AG∣G that would support insertion at proto-splice sites. In fact, all nG∣G sites are enriched in the vicinity of the cleavage site. Additional analyses support an alternative scenario in which exon-shuffling is largely responsible for such excess of phase 1 introns. [Copyright &y& Elsevier]

Analysis of the exon–intron structures of 2208 human genes has revealed that there is a statistically highly significant excess of phase 1 introns in the vicinity of the signal peptide cleavage sites. It is suggested that amino acid sequences surrounding signal peptide cleavage sites are significantly enriched in phase 1 proto-splice sites and this has favored insertion of spliceosomal introns in these sites. [Copyright &y& Elsevier]