Fig. 2. Maintenance of Y′ telomere in humanized yeast. (A) Schematic representation of yeast telomeres associated with a Y′ subtelomeric element, the position of the invariable XhoI (X) site is reported. Digestion of genomic DNA by XhoI allows to measure the size of the terminal fragment of all Y′ telomeres in the cells. The different probes used for Southern blot analysis are shown. The length of the distal repeats was estimated by subtracting 1200 nt from the measured length of the terminal XhoI fragment. (B) Example of Y′ telomere Southern blot hybridized successively to a T2AG3, TG1–3 or Y′ probe. The number of generation after germination is indicated for the Hy cells. Lanes a, d and g: Y cells; lanes b, e and h: Hy cells after 50 generations (early passages); lanes c, f and i: Hy cells after 500 generations (late passages). (C and D) The XhoI blots were hybridized with the Y′ probe. wt: wild type for the RAP1, RIF1, RIF2 and TEL1 genes. In (B–D), the molecular weight markers, used to measure the mean telomere lengths, are indicated in nt. In (C) and (D), the length of distal repeats is indicated at the bottom of each lane.