EXPERIMENTAL FIGURE 6-16 Screening of a yeast genomic library by functional complementation can identify clones carrying the normal form of a mutant yeast gene. In this example, a wild-type CDC gene is isolated by complementation of a cdc yeast mutant. The yeast genomic library prepared as shown in Figure 6-15 is transformed into a ura3⁻, temperature-sensitive cdc mutant strain. The relatively few transformed yeast cells, which contain recombinant plasmid DNA, can grow in the absence of uracil at 23 °C. When these colonies are replica-plated and incubated at 36 °C (a nonpermissive temperature), only clones carrying a library plasmid that contains the wild-type copy of the CDC gene will survive. LiOAC = lithium acetate; PEG = polyethylene glycol.