Recent research: "Aging has many different causes, says Jessica Tyler, a molecular biologist at the University of Texas MD Anderson Cancer Center in Houston. Now, Tyler and her colleagues think they have uncovered yet another way cells age - by losing histones. Histones are important proteins that form a spool upon which DNA is wound. This spooling allows yards of DNA to fit inside a cell and also helps control how genes are turned on and off. Tight winding helps keeps genes off, while loosening the packaging allows genes to be turned on. As yeast cells age they make fewer histone proteins, Tyler's team found. ... Exactly how histones determine how long yeast will live is still unknown. The researchers think falling levels of histones during aging may loosen DNA and allow many genes to be turned on inappropriately. That excess gene activity may zap a cell's energy reserves. Making extra histones may help old yeast keep tighter control of gene activity. ... the team found that the histone life-extension process is likely independent of other known mechanisms for increasing life-span. For instance, histones appear to work differently from the well-known antiaging sirtuin protein Sir2. ... Yeast on restricted-calorie diets live longer. So do yeast with more histones. If the two mechanisms are entirely independent of each other, combining the two treatments should add up to make yeast live longer than either manipulation alone. Instead, combining the treatments in the new experiments led to a life-span extension somewhere in between the solo effect of either treatment. The finding serves as a reminder that biological processes are complicated and intertwined."