Activation of the DNA damage checkpoint occurs in <i>cdc9-1</i> cells at 26°C and is required for their telomere length phenotype.

<p>(A) The <i>cdc9-1</i> mutation leads to accumulation of late S/G2 cells at 26°C. (B) Rad53 activation in response to <i>cdc9-1</i> at 26°C, or after treatment with either hydroxyurea (200 mM, <i>HU200</i>), or Phleomycin (5 µg/ml, <i>PHL5</i>) for 2 h at 26°C. (C) Epistasis analysis of telomere lengthening (assayed by teloblot) in response to <i>cdc9-1</i> involving mutations in genes for different components of the DNA damage signaling network. Telomere length analyses by teloblots which are shown either as sets of four samples representing four spore progeny from the same tetrad or sets of six spores from different tetrads but the same parental strain (for <i>mec1</i> and <i>rad53</i>), with telomere length equilibrated at 26°C. DNA standards (in kbp) shown at left.