Brice Quenoville wrote:
> 1/Is the so called GT-AG rule stating that all eukaryotic
> nuclear introns begin with a GT and finish with a AG
> believed to be that universal or not? If yes would these GT
> and AG always be excised when going to cDNA or can they (or
> part of them) be part of it?
GT-AG exon-intron junctions are consensus sequences. Therefore,
not ALL introns start with GT and end with AG, but they nearly
always do (see Mount S.M. Nucleic Acids Research 10 (1982),
459-472). Splicing will always leave these splice donor and
acceptor sites out of the mRNA (the cell will not make cDNA, that
is what we do in our labs)
> 2/Is it possible that, searching for a reading frame, a
> codon triplet would begin at the end of one exon and finish
> at the beginning of the next or is each exon a complete
> succession of codons (I would guess so but)?
Yes that is very well possible. Why should an exon exist of
complete triplets? So you may find
......AGG TTG Cgt--------intron-------agAT ATT.......
and not necessarily
...... AGG TTG gt--------intron-------ag CAT ATT...........
for the mRNA ........ AGG UUG CAU AUU.........
Louis van de Zande
Popgen
RU Groningen
The Netherlands
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