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Orange-colored S. cerevisiae colonies?

Greg Stuart stuart at niehs.nih.gov
Wed Nov 7 14:31:13 EST 2001

Hello: I occasionally (but rarely) find a bright orange colony on my
agar plates (and perhaps, less frequently, bright yellow cfu?),
plating a Saccharomyces cerevisiae strain. Generally, these colonies
appear after some time on the plates (>2-3 weeks, i.e. in older
cells). I had thought that these orange cfu were likely to be
contaminants, but I encountered recently a large older colony (~5 mm
diameter; yellowish-white - the normal color of my strain) that had
sectors of orange: ~1/4-sectored, plus two or three "spokes" (like the
spoke in a bicycle wheel) of orange, plus a set of 5 closely-grouped
orange spokes (all leading to a common origin slightly off-center from
the colony center). Thus, these orange colonies appear to be arising
de novo, and are not contaminants.

The strain is: TF236, MAT(alpha) ino::HIS3 arg8::hisG pet9(op1)
ura3-52 lys2 cox3::mtarg8 (arg8 mutant allele recoded for
mitochondrial gene expression and inserted into cox3 gene - by Tom
Fox, Cornell). 

My question is: What might be causing this color phenotype? It is
clearly an orange color, not  red (e.g., ade2) phenotype. 

Interestingly, I couldn't find much information (literature, etc.)
regarding orange-colored S. cerevisiae, but happened to stumble
fortuitously across this comment in Table 2 of N. Burns et al.,
"Large-scale analysis of gene expression, protein localization, and
gene disruption in Saccharomyces cerevisiae," Genes & Development 8:
1087-1105 (1994):
Gene: NUC1;
Function: mitochondrial nuclease;
Disruption phenotype: no growth on glycerol; orange colonies.

Thanks, Greg Stuart   :-)

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