Statistical analysis of the exon-intron structure of higher and lower eukaryote genes

Statistics of the exon-intron structure and splicing sites of several diver se eukaryotes was studied. The yeast exon-intron structures have a number o f unique features. A yeast gene usually have at most one intron. The branch site is strongly conserved, whereas the polypirimidine tract is short. Lon g yeast introns tend to have stronger acceptor sites. In other species the branch site is less conserved and often cannot be detemined. in non-yeast s amples there is an almost universal correlation between lengths of neighbor ing exons (all samples excluding protists) and correlation between lengths of neighboring introns (human, drosophila, protists). On the average first introns are longer, and anomalously long introns are usually first introns in a gene. There is a universal preference for exons and exon pairs with th e (total) length divisible by 3. Introns positioned between codons are pref erred, whereas those positioned between the first and second positions in c odon are avoided. The choice of A or G at the third position of intron (the donor splice sites generally prefer purines at this position) is correlate d with the overall GC-composition of the gene. In all samples dinucleotide AG is avoided in the region preceding the acceptor site.