Internal deletion causing gain of function?

E A Greene eagreene at toulouse.inra.fr
Thu Apr 11 12:11:59 EST 1996

Are there any (documented :-) ) examples of nature (rather than genetic 
engineers) deleting some internal portion of a protein coding sequence and 
thus creating a new protein with a new structure and function?

I'm asking this because, in the process of studying a family of plant 
proteins, we find two entries in the database that clearly align with the 
family at their N and C terminal regions but are missing a large section in 
the middle.  The core globular structure (the 3-D structure of one of the 
family members is known) is normally about 100 aas long and in these two 
'abridged' sequences an internal chunk of 40 aas has been removed.  In 
removing those amino acids one loses two beta strands which are essential to 
the known folded structure.

The two 'abridged' sequences (from cDNAs expressed in two different plants) 
while similar, have diverged enough from their common ancestor that one 
_might_ postulate that there's some selective pressure to keep them expressed.

So, we're back to the original question.  One way that nature might create a 
new protein (yes, I'm anthropomorphizing here) is to delete an internal 
portion of a coding sequence and let the new 'abridged' polypeptide chain fold 
in a new way.  Are there any examples of this?

Thanks in advance,

Liz Greene

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