Systematic revelation and meditation on the significance of long exons using representative eukaryotic genomes.

Abstract

Background: Long exons/introns are not evenly distributed in the genome, but the biological significance of this phenomenon remains elusive.

Materials and methods: Exon properties were analyzed in seven well-annotated reference genomes, including human and other representative model organisms: mouse, fruitfly, worm, mouse-ear cress, corn, and rice.

Results: In all species, last exons in genes tend to be the longest. Additionally, we found that (1) canonical splicing motifs are strongly underrepresented in 3'UTR; (2) Last exons tend to have low GC content; (3) Comparing with other species, first exons in D. melanogaster genes demonstrate lower GC content than internal exons.

Conclusions: It cannot be excluded that last exons of genes exert essential regulatory roles and is subjected to natural selection, exhibiting differential splicing tendency, and GC content compared to other parts of the gene body.