ABSTRACT
Several transformation systems for Kluyveromyces yeasts have been described. They make use of chromosomal ARSs or of segments of linear k plasmids. Contrary to many yeast plasmids, such as 2-µm of Saccharomyces cerevisiae which are cryptic in biological function, k1 and k2 confer to killer character to the host cell. The k plasmids can be transferred using the classic yeast transformation technique. Protoplasts are mixed with purified k plasmids in the presence of PEG and regenerated on complete medium. As the k plasmids can be transferred into S. cerevisiae, the question arises whether both killer systems, k and ds RNA, can coexist in the same cell and be functional. A search has been made for ARSs in the k plasmids, using an integrating vector YIp32.51 YIp32 transforms S. cerevisiae and Schizosaccharomyces pombe to LEU± phenotype at low frequency as a result of chromosomal integration.
