Genetic screens have been extraordinarily useful for the identification of protein components that function in a variety of cellular processes. For example, a number of proteins that are necessary for responding to deoxyribonucleic acid (DNA) damage were found in screens for loss-of-function mutants that confer hypersensitivity to DNA-damaging agents (1 ). Genetic screens that report a loss of function can also be used to discern structure-function relationships within a particular protein by providing an assay for loss of function. Combining such an assay with a method that generates mutant alleles of a particular gene can aid in the identification of domains within the encoded protein that are functionally important for the process under investigation. Such approaches are particularly straightforward in unicellular eukaryotes such asSchizosaccharomyces pombe.
