RNA splicing as an error-screening mechanism.

Eukaryote nuclear genes are generally split into coding (exon) and noncoding (intron) regions. During the formation of messenger RNA the introns are precisely excised and the exons religated. A widely accepted explanation for the split structure of eukaryotic genes is that proposed by Gilbert who hypothesized that the division of coding information into small units speeded up the rate of protein evolution by allowing for the recombination of the independent peptide domains encoded by these units ("exon shuffling"). However it has recently become clear that the exon:intron structure of genes most likely preceded the uninterrupted form. This makes it difficult to accept Gilbert's argument as it applies to the origin(s) of split genes since early genes were very inaccurately copied and a highly error-prone system needs less variation not more. Here I propose that split genes and the concomitant process of RNA splicing arose as a mechanism for maintaining the stability of the genetic information in the face of a high level of noise in the gene copier mechanism.