Saccharomyces is a common eukaryotic receptor cell in gene cloning experiments, and it is convenient to cultivate yeast and to cultivate e. coli. There are many kinds of yeast clones. Yeast also has plasmids, and this 2pm plasmid is called 2um plasmid, about 6, 300bp. The plasmids exists in the chromosomes in the nuclei at least a period of time, use 2 PM plasmid and plasmids in e. coli can build to move back and forth between bacteria and yeast cells shuttle plasmid. Yeast cloning vectors are built on this basis.