Yeast vectors for cloning and copper-inducible expression of foreign genes.

The yeast E. coli shuttle vector pMH158 (Figure 1A) is useful for molecular cloning because of the presence of a number of A l X unique restriction sites that allow phenotypic selection of f ;", recombinants in E. coli (1). A smaller derivative of pMH158 41with as much flexibility for cloning and identification of recombinants by phenotypic selection, pYEL2 (Figure 1B), has " set been constructed by the deletion of the 0.6 kb PstI-woI fragment, 7H2kb rejoining the vector ends by treatment with T4 DNA polymerase F and ligase. A further feature of pMH158 and its derivatives is their high copy number in yeast (1), making them attractive for use as expression vectors. The copper-inducible expression cassettes, ' . CUPIB and CUPIE (2) have been cloned into the HindIl-SacI sites of pYEL2 creating pYELC5 (Figure lC) and pYELC7 which is identical to pYELC5 but with reversed multiple cloning B I