The nonuniformity in intron phase distribution, specifically the minimum frequency of phase 2 introns in group II and nuclear introns, suggests their early evolutionary role in exon shuffling.
No immediate clinical impact; leaves open whether phase biases shaped modern exon shuffling.
The distribution of different intron groups with respect to phases has been analyzed. It has been established that group II introns and nuclear introns have a minimum frequency of phase 2 introns. Since the phase of introns is an extremely conservative measure the observed minimum reflects evolutionary processes. A sample of all known, group I introns was too small to provide a valid characteristic of their phase distribution. The findings observed for the unequal distribution of phases cannot be explained solely on the basis of the mobile properties of introns. One of the most likely explanations for this nonuniformity in the intron phase distribution is the process of exon shuffling. It is proposed that group II introns originated at the early stages of evolution and were involved in the process of exon shuffling.
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Fedorov et al. (1992) studied this question.
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