Regarding titering the GAL1 promoter with mixtures of glucose and
galactose: I think that this is going to be very difficult to do in a
controlled way. In such mixtures I would expect a diauxic growth
pattern with consumption of glucose first, then as glucose concentration
falls the GAL1 promoter will become activated.
If you really want to test a range of expression levels, it would be
better to use a gratuitous inducer. Didier Picard's lab has made just
such a system for the GAL1 promoter. They made a construct that is a
fusion of GAL4 DNA binding domain/transactivation domain/estrogen
binding domain of ER. The presence of this protein allows control of
the level of activation of the GAL1 promoter by changing the estrogen
concentration-even in glucose containing media. The basal transcription
rate without estrogen might be a little higher than normal for GAL1
though-I can't remeber if it is significant or not. The paper is in
GENE about two years ago. I don't have the full reference here.
walberg at simmons.swmed.edu