fresh transformations for protein expression??

Csaba Jeney jencsa at
Wed Jan 31 09:18:33 EST 1996


as I read these postings an old experiment came in my mind. It is
nothing about the protein expression but somehow maybe related to the
problem. I just wanted to make maxi preps from very simple plasmids
which do not have any expressable protein but only the beta-lactamase,
and I had to make the preps working very fine, because I needed a
large amount of plasmid DNA. So I was upset when only 1 mg DNA from
500 ml LB was the result...and I have found the same phenomena, if I
used fresh transformants the yield was about 3 mg or higher, when
'old' bacteria was used the yield decreased even below 500 ug per
prep. I did what, seems to me, have done everybody I tried to
reselect, without any success.... I bet that the copy number of the plasmid is decreasing with
time, but why???


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