We have extended the technique of PCR-directed recombination in Saccharomyces cerevisiae to develop a simple method for plasmid or gene construction in the absence of suitable restriction sites. The DNA to be cloned is PCR-amplified with 30-40 bp of homology to a linearized yeast plasmid. Co-transformation into yeast results in homologous recombination at a position directed by the PCR oligonucleotides.

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Combinatorial chemistry has opened a new realm of chemical diversity in the search for useful therapeutics as well as the ability to generate chemical libraries of hundreds of thousands to millions of discrete compounds. For the biologist, the goal is to screen these large libraries quickly and to obtain as much information in the primary screen as possible. Ideally, a primary screen would not only identify potential lead compounds but also yield information about the specificity, toxicity, and potency of that compound. Toward this end, a primary screen has been developed in which two organisms are cocultured, either bacteria, yeast, or mammalian cells, in the presence of a combinatorial library. For example, bacteria and yeast are cocultured either in liquid or in agar. When exposed to compounds from the combinatorial library, individual compounds are found which inhibit bacterial growth antibacterialls, inhibit yeast growth (antifungals), or inhibit both (potential toxins). This screening method is simple, rapid, and eliminates many of the false positives usually encountered in antimicrobial screening.