Are introns just junk?

Christopher Pook Bioc cjp at mbfs.bio.cam.ac.uk
Mon Oct 25 08:51:13 EST 1993


apland at mala.bc.ca (Shannon) writes:

>An article recently printed in the local paper stated: _2 win Nobel for 
>finding most DNA is "junk"_.  The "junk"  they are referring to is the 
>introns found in DNA.  I was taught that introns are useful during 
>the crossover stage of meiosis.  Is this true?  Do Introns serve any 
>functions at all, or are they rightfully labeled as "junk"?

>						First year science student,
>							S.  Apland
An interesting idea that I heard somewhere, although I unfortunately can't 
remember where, was that introns contain an error-checking mechanism which
allows verification of the exon sequences flanking it. The idea came from
a cryptologist/mathematician who tried "cracking the code" of introns and
found a relationship between exon and intron sequences that allowed him to
predict c.70% of the intron sequence from that of the exon. He speculated
that the apparently wasted energy that the cell puts into transcribing
precursor RNA (if the introns role is in DNA recombination or replication
then why include them in RNA??) allowed the cell to verify the transcribed
sequence before translation, thus preventing synthesis of incorrect protein.

This system would therefore be very similar to error-checking protocols used
in communication between computers, where extra "junk??" bytes are added to
the data, their value being determined by some property or relationship with
that data (eg. if the sum of each bit is odd/even add a 0 or 1 respectively).
This allows the recipient to check for mistakes and, I believe, more sophis-
ticated methods can even correct any mistakes detected.

I'd be interested to know what people's opinion on this is. As far as I know
there is no experimental evidence supporting such a hypothesis, such as the 
mechanisms involved, and I certainly heve never heard anything of this before.
I apologise for not being able to recall the names of the originators of this
theory - perhaps someone can enlighten me?

Chris Pook

allowa



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