Hi Colin--
In their nice review 'Foreign gene expression in yeast' (Yeast v8
pp423-488) Romanos et al tell us that "Galactose-inductions can be
carried out in one of three ways: (1) by growing the culture on a
non-repressing, non-inducing ('neutral') sugar, when very rapid
induction follows addition of galactose; (2) by growing the culture in
glucose medium but removing the glucose by centrifugation and washing
the cells before resuspension in galactose medium (this leads to a lag
of 3 to 5 h in induction); and (3) by growing the cells in medium
containing both glucose and galactose, when glucose is preferentially
metabolized before galactose-induction can occur. The first two methods
are frequently used for small-scale but are impractical in large-scale
inductions. It should be noted that many commonly-used strains have
mutations in the galactose permease gene (GAL2) and are not inducible."
I routinely use raffinose or mannose at 2% for a neutral fermentable
carbon source; maltose might work too. Growth on ethanol is better for
my strains than on glycerol, so check out your strain's behavior before
committing yourself. For the glu+gal approach, try 0.2% each and
monitor the time-course of induction. The results are likely to be
gene-specific.
Good luck!
Arle
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a.k.a. Dr. Arthur L. Kruckeberg
Department of Biological Chemistry
UCLA School of Medicine
Los Angeles CA 90024
(310) 825-8363 FAX (310) 206-5272
e-mail kruckeba at biovx1.biology.ucla.edu
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