Figure 2.

Telomerase activity during the life span of a chicken embryonic fibroblast culture. (A) Growth curve for culture 2 (see text) showing the cumulative increase in population doubling with time in culture. (B) Telomerase activity at various population doublings for culture 2. Lane 1, control reactions in which buffer rather than extract was used in the telomerase extension reaction. Lanes 2, 3, and 15, RNase A-treated extracts from chicken embryonic fibroblasts at population doubling 6 (lane 2) or embryo tissue [(Emb) lanes 3 and 15]. Lanes 4 and 14, extract made from embryo tissue, no RNase A treatment; lanes 5–13, 16, and 17, extracts made from chicken embryonic fibroblasts throughout the lifespan of the culture, no RNase A treatment. The population doubling at the time of isolation is given at the top of each well. Thirty micrograms of protein was used in each telomerase extension reaction for lanes 2–13, and 80 μg was used in lanes 14–17.