Figure 3.
SIR2, but not SIR4, is required for longevity in diploid cells. (A) Diploid life span is not regulated by SIR4. Life spans were determined for W303R/W303R, the isogenic derivative, sir4Δ/sir4Δ, W303R MATα, and W303R MATa. Mean life spans and the number of mothers examined were as follows: W303R/W303R 18.2 (n = 49), sir4Δ/sir4Δ 18.1 (n = 50), W303R MATα 21.1 (n = 50), and W303R MATa 20.5 (n = 50). (♦) W303R/W303R; (█) sir4/sir4; (▴) W303R MATα; (×) W303R MATa. (B) Homozygous mutation of sir2 causes a significant reduction in diploid life span. The sir2Δ/SIR2 heterozygote has a life span that is intermediate between the wild-type diploid and the sir2Δ/sir2Δ homozygote. Life spans were determined for W303R/W303R, and isogenic derivatives, sir2Δ/SIR2, and sir2Δ/sir2Δ. Mean life spans and the number of mothers examined were as follows: W303R/W303R 18.8 (n = 50), sir2Δ/SIR2 14.0 (n = 47), and sir2Δ/sir2Δ 12.1 (n = 48). (♦) W303R/W303R; (█) sir2/SIR2; (▴) sir2/sir2.