samik at hhmi.ucla.edu
Sat Aug 6 16:04:57 EST 1994
I am taking a class in introductory genetics. On my last midterm there
was a problem in which the the professor described the following
situation and then ask us, the students, to describe the mechanism by
which it might occur.
The situation is as follows,
"In a single stranded DNA virus, one gene E is found to lie completely
within the bounderies of a second gene D. These two genes produce
different protein products that have no common amino acid sequence,
despite that fact that all of the DNA for gene E is also part of the DNA
for gene D. Briefly suggest an explanation consistent with the data given"
I figured that gene E is simultaneously a gene in own right and intron
releative to gene D. The professor replied "Introns are ONLY in
eucaryotes" which is incorrect, I know that adenoviruses among others
have alternative splicing. However is the mechanism I described even
possible? I looked it up a couple of books(Genes V, Molecular Biology of
the Cell and Molecular Cell Biology). I couldn't find anything in there
but I remeber hearing another professor one time mention something sorta
like what I wrote, but then again maybe that's just wishful thinking on
I now realise that single stranded DNA virus essentially infect bacteria
but I figure that this is an introductory genetics course and I shouldn't
be held resoponsible for what viruses infect what kinds of cells. So let
me rephrase my question, assuming this was a double stranded DNA virus,
would this mechanism be possible.
The "correct" answer was that the two genes have two different start
sites with two different reading frames.
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