ade3 mutants in an ade2 background are white, not khaki. The red pigment in
ade2 mutants seems to derive from an intermediate in purine biosynthesis,
probably a derivative of AICAR. ade3 mutants cannot make fGAR or fAICAR as
they lack the one-carbon units.
I have never been precisely sure why petites in an ade2 background are so
white. I don't think the color reflects the absence of cytochromes, but
rather it reflects again the inability to make purine precursors without
functional mitochondria. Not precisely sure why that is so, and I admit I
am embarrassed that I can't readily figure it out. Perhaps someone can help
on that point.
Michael Andres McMurray <mmcmurra at u.washington.edu> wrote in message
news:805uan$469 at net.bio.net...
> I know that petites often are white even in an ade2 background, but it's
> also true that even in ADE2 backgrounds, colonies or patches of petites
> look whiter (less "creamy"). I think I was once told this is because of
> the loss of mitochondrial cytochromes... any validation to this
> hypothesis, or ideas to the contrary?
>> To get at the point another way, I found some EMS mutants that are just
> plain whiter (less creamy) on rich media. One is a petite, others are
> not. None has an obvious growth defect on rich media. Has anyone heard of
> mutations that change the appearance (in terms of "creaminess") of
> cerevisiae strains?
>> Thanks,
> Michael
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