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
>proposition.
>>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
>examiner...
>----------------------------------------------------------------------
>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
