Yuzuru Iimura

Yeast transformation without the spheroplasting process.

A plasmid, YRp7, carrying the yeast TRP1 gene transformed a trpl strain JH of Saccharomyces cerevisiae without spheroplasting. The transformation conditions were that intact cells were incubated with the plasmid DNA in chilled CaCl2 solution and then the incubation temperature was raised. The transformation frequency changed markedly with the CaCl2 concentration of the solution and the temperature rise after incubation at 0. The optimal CaCl2 concentration and temperature for strain JH were 200 mM and 37, respectively. Polyethylene glycol and the age of cells showed little effect on the transformation. The highest transformation frequency obtained was 300 colonies per μg plasmid DNA, and this was comparable to that obtained with the JH strain by the conventional method using spheroplasts. Transformation was confirmed genetically.