FIG. 4.

DNA damage checkpoint activation in Yku⁻ cells correlates with short telomeres. Total RNA was extracted from the cells tested in Fig. 3A and transferred to nylon membranes. The membranes were successively probed to detect RNR2, RNR3, and actin transcripts. To correct for RNA loading, the signals specific for the RNR transcripts were normalized to the actin signal. The RNR transcript levels were arbitrarily set at 1 in the wt cells grown at 23°C, and RNR transcript levels in Yku⁻ mutants were determined accordingly. The migration positions of the 25S rRNA (3,392 nucleotides) and 18S rRNA (1,798 nucleotides) are indicated as molecular weight references. G, generations.