Figure 1.

Chp1 and Mis6 silence distinct centromeric domains. (A) mis6-302 specifically alleviates central core silencing, but not silencing of the outer repeats. (B) Chp1, like Clr4, Rik1 and Swi6 is required for silencing of the outer repeats, but not the central core. For both A and B, competitive radioactive PCR was performed on cDNA generated by RT–PCR from strains with ura4⁺ (U) inserted within the central core (site 9), the inner and outer repeats of centromere 1 (sites 6 and 13) or in euchromatin (R.Int::ura4⁺) and a fully expressed ura4–DS/E minigene (L) at the ura4 locus. Separated PCR products were quantified. Levels of ura4 (U) were normalized to ura4–DS/E (L) in the mutant strains and expressed relative to values obtained for the wild-type background for each insertion site. In A, mis6-302 and wild-type strains were grown at 25°C, or shifted to the nonpermissive temperature for 4 hr prior to RNA extraction.