Re: Does the Importance of Introns go against the one gene-one protein theory?

Hi Heather, 
thank you for your question! 
I'm going to assume that your textbook contains an explanation of 
introns, exons, and splicing, so I won't go into that here.  However, I 
think it's important to realize where Beadle and Tatum were coming from when 
they arrived at their theory, because it was truly groundbreaking in their 
day and it's still valid in many ways.  I don't know if your textbook goes 
into any science history,  but Beadle and Tatum were researching the 
connection between metabolic errors and enzymes, which are a special type of 
protein (gene product).  They used a bread mold called Neurospora for their 
experiments, and, using x-rays to cause genetic mutations, they generated 
mutant strains of the mold that were unable to carry out specific metabolic 
functions.  They found that the mutations were inherited as single genes, 
and that each metabolic defect was caused by the loss of a single enzyme.  
As it was known from prior research that each biochemical reaction in a 
metabolic pathway is regulated by a single enzyme, B and T reasoned that the 
production, and therefore the activity, of the enzyme must be controlled by 
a single gene.  This research was taking place back in the days when 
scientists were just figuring out that DNA was the information-bearing 
molecule in the cell, so the work of Beadle and Tatum was really the first 
time anyone directly showed a correlation between GENOTYPE and PHENOTYPE.  
As you may know, they won the Nobel Prize in 1958 for their "one gene--one 
enzyme" hypothesis.  Later, this was modified to "one gene--one 
polypeptide", when people realized that many functional proteins actually 
consist of more than one polypeptide "subunit". 

Of course, nothing was known about the mechanism of gene transcription and 
translation at that time.  Your question directly addresses the mechanism of 
"alternative splicing", whereby a given DNA sequence can encode the 
information for making more than one messenger RNA, and hence more than one 
protein.  However, even though alternative splicing can generate multiple 
proteins, they are all very similar to one another, and can be considered 
variations of a basic blueprint.  For example, a number of growth factors 
(called FGFs) which are active during embryonic development are products of 
alternative splicing, but these proteins are so similar to one another that 
one can actually substitute for another in certain developmental situations.  
There are other examples of the similarities outweighing the differences 
with these products of alternative splicing, as well, so when you 
consider all that, were Beadle and Tatum really so wrong??  Personally, I 
think there is more than one right answer to this question, depending on how 
you look at it.  I hope that you'll have some interesting discussions in 
your class about this topic after everyone receives their answers from the 
internet. Please write back if I can be of further assistance.

One more thing, if you're interested:  the following website contains the 
presentation speech for Beadle and Tatum's Nobel Prize, which includes a 
summary of their research--I think it might help to give some perspective on 
how their theory contributed to the field of genetics.
 
 http://
nobel.sdsc.edu/medicine/laureates/1958/press.html

Warm Regards, 

Jen