Figure 6. Sgo2 forms a transcriptionally repressed chromatin domain distinct from Swi6/HP1 heterochromatin.

(a) The absence of Sgo2 and Swi6 has different effects on the repression of subtelomeric genes. The RNA level of the ura4⁺ gene in each strain was analysed by quantitative reverse transcriptase–PCR (RT–PCR); left, endogenous ura4⁺; middle, ura4⁺ inserted at 7 kb from tel2R; right, ura4⁺ inserted at 52 kb from tel2R. Each value of ura4⁺ relative to that of his1⁺ was re-normalized to the wt value. Error bars indicate the s.d. (n=3). (b) RNA expression of the ura4⁺ gene in bub1Δ and set2Δ cells was analysed as in a. (c) Growth assays of the strains used in a and b. Dilution series of cells were spotted on YES (non-selective complete medium), SD-uracil (lacking uracil) and 5-FOA (YES with 1 mg ml⁻¹ 5-fluoroorotic acid, the counter-selection drug for ura4⁺) plates at 32 °C for 2 days unless otherwise indicated. The ura4Δ strain (top) was the control for the assay. It is noteworthy that 5 days incubation was necessary to see growth on 5-FOA for 52 K:ura4⁺ due to the lower level of gene repression as compared with the that 7 K:ura4⁺.