Are introns just junk?

Arthur Kania ak990140 at SPECIALK.IAIMS.BCM.TMC.EDU
Sat Oct 23 11:23:13 EST 1993


In article <1993Oct22.201441.2618 at malins.mala.bc.ca>, 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
> 

It has been proposed that introns and other junk DNA actually serve some purpose. 
Recombination is one of them: it turns out that a lot of proteins have particular
functional domains confined to specific exons. Evolution can take advantage of
that by shuffling the exons around (unequal recombination etc...) and creating
new proteins. 
Introns also contain regulatory sequences which control when and where the
particular gene will be expressed. In addition, there are specific splicing
signals within introns, which help to get rid of the intronic sequences from the
transcribed RNA. Splicing can also be thought of as a regulatory mechanism:
through alternative splicing (using different intronic signal sequences) the same
gene can encode for a number of different proteins.
The other "junk" DNA, found outside of exon/intron groups, is also pretty
interesting. It was proposed that it contains DNA replication origins and binding
sites for proteins which make up the chromosome "scaffold".
There is probably lots of other stuff that I didn't mention; you should read some
chapters from Molecular Cell Biology (Darnell, Lodish and Baltimore) or another
basic cell bio textbook.

Arthur Kania
Inst. for Molecular Genetics
Howard Hughes Medical Inst.
Baylor College of Medicine 
Houston, TX 
-- 
A. Kania
Institute for Molecular Genetics
Howard Hughes Medical Institute
Baylor College of Medicine



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