Kathy Baynton baynton at
Thu Apr 30 06:05:07 EST 1998

Hi everyone!

I was wondering if anyone out there knows of a reference or has any
information on how suppression of mutant genes carrying stop codons 
works in S. cerevisiae; is it an all or nothing effect?  Or are there
degrees of suppression?  The reason I am asking is that I had a surprise
not too long ago with a segregant from a cross between one parent
carrying a suppressible mutation in an auxotrophic marker and a second
bearing normally a mutation in another gene in the same pathway, but
that I know of, not suppressible (in fact, this is another question: 
does anyone know of the nature of the trp1.4 mutation?  I know it is a
point mutation, but does it result in a stop codon?)  Anyways, I tested
this segregegant several times for the trp- phenotype; each time it
responded negative, which caused me to think that it had the other
mutation.  I found, however, that after transforming this strain with a
plasmid carrying the TRP1 marker, that none of what I originally thought
were transformants have the plasmid; these all appear to be "revertants"
(via suppression).  I would really like to know how this works and how i
could have missed this during the initial screens.  Any information you
might have would be greatly appreciated!!


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