> Most probably you just picked the satellite colony (non-resistant = not
> baring a plasmid) that grown after amp has broken down in the medium due to
> overincubation. Amp is not very stable and will brake down at 37C over a few
> days. Take the original plate, wash of all the cells from the surface and
> re-streak (or better, spread) a portion on a fresh amp plate. Next day pick
> the resistant colonies. Otherwise, you may try to pick the largest colonies
> from the original plate: most probably these are (were!) the
> plasmid-containing ones.
. . . definately "spread" an aliquot. That way you will get a population
including all the types of plasmid in your experiment (I am assuming it is
a transformation of a ligation mixture). Regards, Mike.
