A yeast assay for functional detection of mutations in the human cystathionine {beta}-synthase gene

Mutations in the human cystathionine ß-synthase (CBS)gene are known to cause homocystinuria and may also be a significantrisk factor for premature atherosclerosis. We have previouslyshown that the human CBS protein can substitute for the endogenousyeast CBS protein in Saccharomyces cerevisiae. We now show thatexpression of three different CBS mutants known to be associatedwith reduced enzyme activity in humans fail to complement growthin the yeast assay. in addition, we have used the yeast CBSassay to identity eight mutant CBS alleles in cell lines frompatients with CBS deficiency. These mutant alleles include twopreviously identified and five novel CBS mutations. Our resultsalso demonstrate that the yeast CBS assay can detect a largepercentage of individuals heterozygous for mutations in CBS.This system should be useful in determining the relationshipbetween CBS mutations and human disease.