This chapter describes the use of genomic and cDNA banks to isolate specific genes by complementation in Saccharomyces cerevisiae. The most straightforward approach to cloning genes from plasmidborne banks is complementation of a recessive marker. A recipient strain is constructed that carries a recessive mutation in the gene of interest as well as a nonreverting null allele of the chromosomal cognate of the selectable marker carried on the plasmid vector, This strain is then transformed with pools of plasmids from a bank constructed from wild-type genomic DNA. Transformants are recovered by selecting for eomplementation by the vector-borne selectable marker. Cloning genes that are defined by dominant alleles is a straightforward extension of cloning by complementation of recessive alleles. The only difference is that the clone bank has to be constructed de novo from genomic or cDNA prepared from the strain carrying the dominant mutation. In the absence of any direct information about the identity of a gene or its gene product, one recourse is to isolate a set of genes whose regulation fulfills some interesting set of criteria. One approach to achieving this end has been to clone random genomic fragments into a plasmid carrying an enhancerless promoter that drives expression of a readily scored gene, such as lacZ. Random transformants are then examined for conditional expression of lacZ in response to the desired signal.
All Science Journal Classification (ASJC) codes
- Molecular Biology