FIG. 3.

Silencing conferred by the TD is Sir dependent. The assay system is described in the legend to Fig. 2. In strains with deletions of SIR2, SIR3, or SIR4, GBD-TD fails to establish silencing at a weakened HMR locus. Silencing, however, does not require the SIR1 gene. The Ade⁻ phenotype of the sir2Δ, sir3Δ, and sir4Δ strains confers their dark color; the sir1Δ stain is Ade⁺.