The host range of the pKD1-derived plasmids in yeast

pKD1 is a 2 mu-like circular plasmid found in the yeast Kluyveromyces drosophilarum that can also stably replicate in Kluyveromyces lactis. We have found a short intergenic region in this genome that appears to be functionally neutral; that is, the introduction of foreign sequences into the single EcoRI restriction site located near one of the inverted repeats did not affect the high stability of the natural plasmid. By introducing a G418 resistance gene at this site, we constructed an autonomous recombinant plasmid. Since this vector did not require cir+ hosts for its stable maintenance, it could be used to examine the transformation host range of pKD1 among all the species belonging to the genus Kluyveromyces. Both species closely related to K. drosophilarum as well as a few other species that are very different in chromosomal GC% could be transformed to yield highly stable transformant clones.