Figure 1. Schematic explanation of the genetic screen carried out.

A double mutant elg1 ctf4 strain is kept alive by the presence of a plasmid carrying the ELG1 gene. The ADE3 marker on the plasmid confers a red pigment to the cells carrying it. As these cells are unable to lose the plasmid during colony formation, all colonies are uniformly red. This strain was transformed with a high copy number library carrying random fragments of the yeast genome. Cells that received a plasmid that suppresses the synthetic lethality phenotype can now lose the ELG1-containing plasmid, becoming white. These cells create white or red/white sectored colonies.