Exon shuffling by recombination between self-splicing introns of bacteriophage T4.

The organization of genes into exons separated by introns may permit rapid evolution of protein-coding sequences by exon shuffling. Introns could provide non-coding targets for recombination, which would then give rise to novel combinations of exons. Evidence to support this theory is indirect and consists of examples of homologous domains of protein structure encoded in different genes, with introns in conserved positions at the boundaries of these domains. Here, we report the first direct evidence for exon shuffling. Two spontaneous deletion mutations of phage T4 have been characterized by sequencing, and they are clearly the result of recombination between homologous regions of two self-splicing group I introns. As a result of the recombination, exons of different genes are transcribed together, with a hybrid intron between them. One of these introns is proficient in self-splicing.