Primordial spliceosomal introns were probably U2-type.
The two types of eukaryotic spliceosomal introns, U2 and U12, possess different splice signals and are excised by distinct spliceosomes. The nature of the primordial introns remains uncertain. A comparison of the amino acid distributions at insertion sites of introns that retained their positions throughout eukaryotic evolution with the distributions for human and Arabidopsis thaliana U2 and U12 introns reveals close similarity with U2 but not U12. Thus, the primordial spliceosomal introns were, most likely, U2-type.
Basu
Malay Kumar
MK
National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, 8600 Rockville Pike, Bethesda, MD 20894, USA.
Rogozin
Igor B
IB
Koonin
Eugene V
EV
D000818:Animals; D017360:Arabidopsis / Q000235:genetics; D001483:Base Sequence; D019295:Computational Biology; D019143:Evolution, Molecular; D006801:Humans; D007438:Introns / Q000235:genetics*; D008954:Models, Biological; D008969:Molecular Sequence Data; D017381:Spliceosomes / Q000378:metabolism*