In the absence of Rnr1 telomeres cannot become elongated by increased telomerase activity.

<p><b>A)</b> Telomere length analysis by Southern blotting shows that mutations of the long <i>TLM</i> genes <i>PIF1</i> or <i>ELG1</i> cause telomere elongation when introduced in a wild type background but do not affect the short telomere length of <i>rnr1</i>Δ <i>crt1</i>Δ mutants. Telomere blots were performed approximately 200 generations after the long <i>tlm</i> mutation has been introduced. Represented are biological replicates of the indicated strains. <b>B)</b> Telomere length analysis by Southern blotting of cells expressing Cdc13-Est1 and Cdc13-Est2. Expression of the fused proteins results in telomere elongation in wild type cells and <i>crt1</i>Δ mutants but not in <i>rnr1</i>Δ <i>crt1</i>Δ mutants or <i>rnr1</i>Δ <i>crt1</i>Δ <i>elg1</i>Δ mutants. A plasmid expressing Cdc13 was used as a control and did not cause elongation of wild type cell telomeres. Represented are biological replicates of the indicated strains approximately 200 generations after transformation of the indicated plasmid.