Plant circadian clocks increase photosynthesis, growth, survival, and competitive advantage

Circadian clocks are believed to confer an advantage to plants, but the nature of that advantage has been unknown. We show that a substantial photosynthetic advantage is conferred by correct matching of the circadian clock period with that of the external light-dark cycle. In wild type and in long- and short-circadian period mutants of Arabidopsis thaliana, plants with a clock period matched to the environment contain more chlorophyll, fix more carbon, grow faster, and survive better than plants with circadian periods differing from their environment. This explains why plants gain advantage from circadian control.     

Genetic analysis of histone H4: essential role of lysines subject to reversible acetylation

The nucleosome is the fundamental unit of assembly of the chromosome and reversible modifications of the histones have been suggested to be important in many aspects of nucleosome function. The structure-function relations of the amino-terminal domain of yeast histone H4 were examined by the creation of directed point mutations. The four lysines subject to reversible acetylation were essential for histone function as the substitution of arginine or asparagine at these four positions was lethal. No single lysine residue was completely essential since arginine substitutions at each position were viable, although several of these mutants were slower in completing DNA replication. The simultaneous substitution of glutamine for the four lysine residues was viable but conferred several phenotypes including mating sterility, slow progression through the G2/M period of the division cycle, and temperature-sensitive growth, as well as a prolonged period of DNA replication. These results provide genetic proof for the roles of the H4 amino-terminal domain lysines in gene expression, replication, and nuclear division.     

Increase in activity during calorie restriction requires Sirt1

Sir2 (silent information regulator 2) is a nicotinamide adenine dinucleotide-dependent deacetylase required for longevity due to calorie restriction in yeast and Drosophila. In mammals, calorie restriction induces a complex pattern of physiological and behavioral changes. Here we report that the mammalian Sir2 ortholog, Sirt1, is required for the induction of a phenotype by calorie restriction in mice.