In yeast, worms, flies and even certain mammals, a reduced-calorie diet extends lifespan, but the biochemical mechanisms underlying this process have been unclear. In 18 July Nature, Su-Ju Lin and colleagues from Massachusetts Institute of Technology, Cambridge, US, show that calorie restriction (CR) extends Saccharomyces cerevisiae lifespan through increasing respiration by up to a factor of three (Nature 2002, 418:344-348).

Lin et al. used a model of calorie restriction in the budding yeast S. cerevisiae and observed that CR activates SIR2 to extend yeast's lifespan. SIR2 encodes an enzyme that removes acetyl groups from the histones involved in packaging DNA, and probably exerts its effect on lifespan by suppressing transcription. In addition they show that shunting of carbon metabolism toward the mitochondrial tricarboxylic acid cycle and the concomitant increase in respiration play a central part in extending the life of these cells.

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