is there a shelf-life of x-gal stock? - (Jul/02/2006 )

hi all

i recently bought puc19 dna, and thought of making a stock of my own before i started using it. so i transformed e coli cells with the vector (native, no insert, as supplied by company), and plated on amp+ agar with x-gal and iptg spread over as required.

the result was that i got an excellent growth of bacteria, but all white. the fact that they grew on the amp+ medium is evidence of transformation, but why the white colonies. there was no insert, and so the colonies should have been blue.

what could the reason be.

the iptg i had prepared fresh, but the x-gal stock was about 6 weeks old.

- viv

how was they stored? I keep them at -20° for month without pb.
IPTG in water. Xgal in formamide.