Transformation of Lithium-Treated Yeast Cells and the Selection of Auxotrophic and Dominant Markers

Transformation of yeast cells can be achieved using lithium-treated or spheroplasted cells. Spheroplast transformation (1 ,2 ) is a high efficiency method yielding up to 10⁴ –10⁵ transformants per �g of DNA (but more typically, in practice approximately 10³ per �g). The preparation of spheroplasts, however, is somewhat laborious and tedious. The transformed spheroplasts require plating in a soft agar overlay to allow cell wall regeneration; additionally, the generation of undesired polyploids through protoplast fusion is also a possibility. In contrast, the lithium acetate method is relatively quick and simple to perform. It has the advantage that the cells remain intact, and so do not fuse, and can be plated directly onto the surface of selective agar plates. The transformation efficiency generally is similar to the spheroplast method.