ura3 mutant yeast strain grows on SD-uracil- - (Oct/11/2012 )

hello,

ı have a yeast strain (W303-1A) which is ura3 mutant. thus ıt does not grow on SD-uracil medium.

two days ago first I inoculated to YPAD medium and incubated at 28 degree overnight. after that ı used this culture for inoculation to SD - uracil medium. after overnight incubation the yeast growth.

what is the problem. Do you have any idea about this case.

thanks.

Three possibilites:
1) Your medium is not really ura-
2) Your yeast is not ura-
2a) A rare but possible mutation restored ura+ to your strain.

I'd vote for a contaminant ura+ strain, but check the medium with a verified ura- strain.