blue on glucose X-gal

M.Roeters at M.Roeters at
Mon Oct 30 05:45:36 EST 2000

hello everyone, I am using a brent 2-hybrid screening to find binding 
proteins in a DNA-library. I use EGY48 yeasts and I transfected the bait and 
prey (library) and a lacZ reporter (pJK103 or psH18-34). I found colonies 
growing on gal plates lacking his/ura/trp/leu. I plated these "binding 
protein" yeasts on gal X-gal HUT- and on glu X-gal HUT- for a blue/white 
screening. the result was really strange: the colonies turned blue on the 
plates with glucose (the prey should not be present since tehere is no gal) 
and white on the gal plates. I repeated this several times, and I know that 
the plates are right. I try to make sure that the gal promoter is turned off 
when I plate the yeasts on the X-gal plate. I also performed a growth/no 
growth screening on glu HUTL- and gal HUTL- and again the results are not as 
aspected. has anyone experienced this? if you know what the problem is, 
please e-mail me:  mroeters at (Marjolijn)


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