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
Research 21:2315-2322].
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.
Amicalement,
Laurent
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Laurent Duret duret at biomserv.univ-lyon1.fr
Tel: +33 72.44.81.42 Fax: +33 78.89.27.19
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
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