In article 01HJZDT423DE0005SY at PLAINS.UWYO.EDU, FERDIA at UWYO.EDU ("KIRK A. ADAMS") writes:
> I suspect this high sequence conservation among the introns indicates a
> functional importance.
There are evidences that non coding regions may have crucial functions. In a
recent work I have surveyed non-coding regions that remained highly conserved
during vertebrates evolution (300 - 450 Myrs) [Duret et al. 1993 Nucl. Acids
Highly concerved regions (> 70% similarity over 100 to 1450 nt)[HCR], in non-coding
regions of genes that diverged more than 300 Myrs ago are surprisingly frequent.
I found many cases where conservation was higher in HCR than in coding regions.
Potential functions of these HCR are discussed.
> Nakashima et al., however, suggest no function due to
> the lack of significant secondary structure found by GENAS system analysis.
> They propose an "accelerated evolution" among the exons. I am skeptical of
> this since I know of no mechanism that accelerates gene mutation rates
> (especially between exons vs. introns).
Such "accelerated evolution" is possible if there is a selection for protein
polymorphism (such as for MHC genes). To test this you should compare evolutionary
rate in introns, codons synonymous sites (silent sites) and non-synonymous sites.
If there is a selection for polymorphism, you should find a higher evolutionary
rate at non-synonymous sites than silent sites or introns.
If evolutionary rate is much higher at silent sites than in introns, then introns are
likely to be functional.
Laurent Duret duret at biomserv.univ-lyon1.fr
Tel: +33 188.8.131.52 Fax: +33 184.108.40.206
Laboratoire de Biometrie, Genetique et Biologie des Populations
Bat 741 - URA CNRS 243 Universite Claude Bernard - Lyon I
43, Bd du 11 Novembre 1918
69622 Villeurbanne cedex FRANCE