Figure 1.

Genetic screen for mutants defective in heterochromatic silencing. (A) Schematic representation of the screening strategy. High-throughput crossing of a gene deletion library to a tester strain (see text for further details) facilitated analysis of the effects of individual gene deletions on silencing of an ade6 ⁺ reporter gene inserted into the centromeric outer repeats of centromere 1 (cen1:ade6 ⁺; otr (dg and dh): outer repeats; imr: innermost repeats; cnt: central core) (B) Illustration of the semi-quantitative system used to score defects in cen1:ade6 ⁺ silencing, based on colony colour on plates containing limiting levels of adenine (LOW ADE) or colony size on plates lacking adenine (-ADE), where 4 is equivalent to wild-type silencing, and 1 indicates strong ade6 ⁺ de-repression.