about introns

awalley at radius.jr2.ox.ac.uk awalley at radius.jr2.ox.ac.uk
Tue May 12 07:48:44 EST 1998

alvaro mailhos wrote:

> >
> Thanks for your answer! I actually found a couple of cases where the
> initial Met is not in the first exon (and here a semantics question: a
> collegue of mine insists that if does not correspond to a coding sequence
> you cannot call it an exon. Is this right?).

<rest snipped>

This is a point that many people don't seem to grasp. The exons are what make
up the mRNA so it is irrelevant whether they have coding or non-coding
in them. Exons are transcribed from the DNA along with the introns and then
introns are spliced out to give the mRNA. The translation step then defines
coding region. Hence your colleague is wrong.

Hope that makes things clearer,

Andrew Walley,
Wellcome Trust Centre for Human Genetics,
Oxford, UK

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