The evolution mechanism of intron length

Within two years of their discovery in 1977, introns were found to have a positive effect on gene expression. Our result shows that introns can achieve gene expression and regulation through interaction with corresponding mRNA sequences. On the base of Smith-Waterman method, local comparing helps us get the optimal matched segments between intron sequences and mRNA sequences. Studying the distribution regulation of the optimal matching region on intron sequences of ribosomal protein genes about 27 species, we find that the intron length evolution processes beginning from 5′ end to 3′ end and increasing one by one structural unit, which comes up with a possible mechanism for the intron length evolution. The intron of structure units is conservative with about 60 bp length, but the length of linker sequence between structure units changes a lot. Interestingly, distributions of the length and matching rate of optimal matched segments are consistent with sequence features of miRNA and siRNA. These results indicate that the interaction between intron sequences and mRNA sequences is a kind of functional RNA-RNA interaction. Meanwhile, the two kinds of sequences above are co-evolved and interactive to play their functions.