We have studied different parameters for efficient DNA transfection in vari
ous cell types and with different size of the promoter. Here we report that
the optimum condition for DNA transfection by electroporation is 350 V/960
muF for PC12, 450V/960 muF C6 cells, and 250 V/500 muF for COS-1 cells. Fo
r the human neuroblastoma (SK-N-SH) cells the optimum condition for DNA tra
nsfection is by the calcium phosphate method. In promoter mapping studies,
a serial deletion approach is commonly used. To optimize transfection we ha
ve selected three DNA constructs that varied in size from 4.5 to 12.4 kilob
ases (kb). We measured the promoter activity of these constructs under cond
itions of 'equal amount', 'equimolar', and 'equimolar plus carrier DNA to m
ake it equal amount'. We recommend that for comparative purpose, transfecti
on should be carried out under 'equimolar condition' without a need to adju
st the total amount of DNA by carrier DNA. Taken together, our results sugg
est that efficient methods for DNA transfection are important to study gene
regulation by devising better ways to deliver DNA into the mammalian cells
.