A rapid, simple, and sensitive method for plasmid copy number comparis
on was developed. The extracted plasmids from the same; amount of cell
s were subjected to agarose gel electrophoresis and the gels photograp
hed. The photographs were processed by a Macintosh image analyser;to e
numerate the densities of plasmid bands. As a size reference, lambda -
DNA digested with a restriction enzyme was used. The densities divided
by size of plasmids (base pair) would represent relative values of th
eir copy numbers.