ROOSSINCK,MARILYN roossinck at aardvark.ucs.uoknor.edu
Thu Oct 6 19:32:00 EST 1994

In article <199410041405.KAA26159 at hobbes>, ogston at HOBBES.KZOO.EDU (Walter Ogston) writes...
>Ed Rybicki makes a comment about evolution of negative strand viruses,
>to the effect that what has evolved must be advantageous because it has
>evolved.  The problem with this proposition is that it is circular, and
>doesn't explain anything interesting.  Nothing against Ed, lots of
>people have done the same thing.  
>The real challenge for the evolutionary biologist is to explain why a
>particular structure or system favors the survival and replication (or
>reproduction) of the organisms that posess it.  Comparison with
>alternatives is important here.  And ideally the explanation should 
>lead to an experiment or observation that will test the explanatory 
>In the case of negative strand viruses, one significant difference from 
>positive strand viruses is that the former can express several different 
>mRNAs on infection, at different levels, whereas the latter can express 
>only one mRNA, and in order to separate different genetic functions early 
>in infection they have to go through the business of separating the
>components of the polyprotein.  
>Furtiher development of this argument is left as an exercise to the
>Walter Ogston				ogston at hobbes.kzoo.edu

Actually, (+) sense viruses can express several mRNAs early, by using divided
genomes, a fairly common strategy in the plant viruses.  They also often use
subgenomic promoters for timed expression.

M.J. Roossinck
S.R. Noble Foundation

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