Figure 3.

The raf gene deletions exhibit centromere-specific silencing defects. (A) A schematic diagram of the centromeric and pericentromeric regions of S. pombe chromosome 1. The relative positions of the ura4⁺ reporter integrants are shown with their corresponding strain designations. The strongest points of repression in cenI correspond to the otr (CYP27), followed by the imr (CYP26) and central core (CYP25) in hierarchical order. Strain CYP28 contains the ura4⁺ reporter at a euchromatic location. Note that strain CYP27 also contains a swi6 deletion, which partially derepresses this strain and sensitizes this background to the effects of other silencing factor mutations. (B) Overnight cultures of raf1Δ and raf2Δ strains in the indicated reporter backgrounds (illustrated in A) were compared with clr4Δ and rik1Δ control strains. Cells were diluted and spotted onto nonselective supplemented EMMG (N/S sections), EMMG lacking only uracil (–Ura sections), or supplemented EMMG containing 1 g/L 5-fluoroorotic acid (FOA sections). Cells were spotted in serial fourfold dilutions.