Figure 2.

Rrm3p affects telomere length and de novo telomere addition but not in the same ways as Pif1p. (A) DNA was prepared from four individual colonies from each strain: PIF1 RRM3, PIF1 rrm3Δ, pif1Δ RRM3, and pif1Δ rrm3Δ cells. The DNA was digested with XhoI, separated by electrophoresis in a 0.7% agarose gel, prepared for Southern analysis, and probed with a C_1–3A/TG_1–3 telomeric probe. The large curly brace indicates the terminal XhoI fragments from Y‘-bearing telomeres. Molecular weight markers are in kilobase pairs. (B) The rate of de novo telomere formation on a YAC was determined using 10 plate fluctuation tests (Lea and Coulson 1949), conducted 2–4 times per strain, as described in Schulz and Zakian (1994). Because Leu⁺ FOA^R cells can also be generated by point mutations in URA3, the sites of telomere addition in multiple independent Leu⁺ FOA^R clones were mapped to determine the fraction of these events that were due to de novo telomere addition. Each filled circle marks the physical end of a YAC in one such colony. Leu⁺ FOA^R colonies that contained a YAC of unaltered length were presumed to arise from point mutations in URA3. Numbers in parentheses indicate the range of values seen in independent experiments. Numbers in brackets are the fold difference relative to the wild-type strain.