white/blue screening problem

wliu at receptor.pharm.uwa.edu.au wliu at receptor.pharm.uwa.edu.au
Wed Oct 9 21:38:09 EST 1996


Hi,netters,
I recently cloned a 0.5 kb size gene into pALTER used for mutagenesis,
when I identified the cells (JM109) with recombinant DNA, I found that
within 12  to 20 hours the colonies appeared a slight blue in the
center and  white around much, on the control plate, the cells with
non-recombinant DNA then appeared in deep blue colour. However, after
24 hours, the colonies with slight blue become blue, only a few white
colonies exsited on the plate. The restriction digestion analysis
confirm that the white colonies are cells with recombinant DNA. How to
explain the slight blue colonies developing deeper blue later? Also,
the plasmid  DNA form this have the same patten of electrophorisis
results( not after restriction digestion) with those from white
colonies. Dose anybody have idea about this?
Thanks
Weihong Liu





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