Determination of gross chromosomal rearrangement rates.

Cells devote a significant amount of metabolism to maintaining the stability of their genome and to preventing inappropriate chromosomal rearrangements that are characteristic of many cancers. A simple genetic assay using haploid derivatives of the yeast Saccharomyces cerevisiae provides a means to quantitatively measure the rate at which gross chromosomal rearrangements (GCRs) accumulate in different genetic backgrounds. This assay measures the rate of simultaneous inactivation of CAN1 and URA3 markers placed on a nonessential end of a yeast chromosome and in principle can be implemented in any haploid strain. Rearrangements detected with this assay include broken chromosomes healed by de novo telomere additions and a spectrum of inter- and intrachromosomal fusion events. The GCR assay allows for detailed analysis of the contributions of individual genes and different pathways in the suppression of genomic instability.