| At least 723 genes contribute to the stability of chromosomes in yeast. While much has been studied about the isolated functions of these single genes, less has been studied about the emergent properties of the system of genes as a whole. To understand these properties, we report novel chromosome instability phenotypes induced by gene over-expression and compare these to the loss-of-function phenotypes that were reported previously. We performed 136 focused assays and report 52 novel chromosome-instability phenotypes. Using imaging flow cytometry, we report that over-expression of genes that promote G1 tend to induce chromosome/marker gain; the genes that promote the later stages of the cell cycle tend to induce chromosome/marker loss. We modeled the biochemical dynamics of a possible mechanism, "mitotic slippage," using a previously published system of differential equations. To systematically explore additional mechanisms, we assayed the growth phenotypes of 252 double mutants; each pair of mutants consisted of one of our gain-of-function mutations paired with a deletion mutation that was previously implicated in chromosome instability. We report that 71 double mutants demonstrated synthetic dosage sickness or lethality, while 22 double mutants demonstrated dosage suppression. Dosage suppression was observed consistently using CDC20, a gene that induced mitotic slippage in silico. Sickness and lethality was induced consistently by the ectopic expression of IME2, REC8, and NDT80, genes that normally function during meiosis. One application for understanding these over-expression phenotypes is the search for drug targets for the chemoprevention of mutagenesis and cancer. |
