Effect of polyethylene glycol in plasmid DNA solution on transformation of CaCl2-treated Escherichia coli cells.

Transformation ofpBR322DNA to Escherichia coli cells treated with CaCl2was stimulated by addition of 8%polyethylene glycol (PEG) 600 to the DNAsolution.Prolonged incubation of the competent cells in chilled CaCl2 solution (Dargert and Ehrlich, 1979) raised the transformation efficiency by a factor of 5.This prolonged incubation did not inhibit the stimulus effect of PEG.WhenPEG600 or PEG1,000 was added to the mixture of plasmid pBR322DNA to a final concentration of 2%and the competentcells were incubated at 0°Cfor 24 hr, weroutinely obtained over 107 transformants per fig of pBR322DNA, and the competent cells transformed comprised 24% of the viable cells.Transformation of recombinant plasmid DNAconstructed in vitro is an important step for genetic engineering.Mandel and Higa1} have reported that Escherichia coli cells treated with chilled CaCl2 solution can be made competent to take up phage DNA.This CaCl2 treatment procedure was used for tranformation with R-factor by Cohen et al2) Recently competent cells treated with CaCl2 solution supplemented with RbCl were used for transformation by Kushner3) and he obtained over 107 transformants of E. coli SK 1590/fig pBR322 DNA.Norgard et al.A) also obtained 107 transformants of E. coli %1 776//ig pBR322 DNAwith modification of the conditions of CaCl2-treatment.Dargert and Ehrlich5) found another simple modification of