Yeast episomal plasmids (YEp) were constructed using

• 2μm yeast plasmid, fragments of yeast nuclear DNA and E coli vector pMB 9
• 2μm yeast plasmid, fragments of yeast nuclear DNA and E coli vector pBR 322
• 12μm yeast plasmid and E coli vector pMB 9
• 12μm yeast plasmid and E coli vector pBR 322