A fluorescent modification of adenosine triphosphate with activity in enzyme systems: 1,N 6 -ethenoadenosine triphosphate

A new, highly fluorescent adenosine triphophate (ATP) analog, 1,N(6) ethenoadenosine triphosphate, has been synthesized. Its fluorescence properties, including the long fluorescence lifetime and the possibility of detection at very low concentrations, in conjunction with its activity in the representative enzyme systems here reported, make it a valuable probe of enzymic mechanism and structure.     

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.     

Hf-W Isotopic Evidence for Rapid Accretion and Differentiation in the Early Solar System

The time scales over which inner solar system objects accreted and differentiated are unclear because the isotopic systems of many meteorites are disturbed. 182Hf decays to 182W with a half-life of 9 million years and is a particularly useful chronometer because both elements are highly refractory and immobile. Tungsten isotopic data for IIA, IIIA, IVA, and anomalous iron meteorites and H, L, and LL chondrites indicate that their parent bodies accreted rapidly and segregated metal within just a few million years.     

A tunnel in the large ribosomal subunit revealed by three-dimensional image reconstruction

A better understanding of the molecular mechanism of protein biosynthesis depends on the availability of a reliable model for the ribosome particle. The application of a diffraction technique, namely, three-dimensional image reconstruction from two-dimensional sheets of the large ribosomal subunits of Bacillus stearothermophilus at a resolution of 30 angstroms is described. The resulting three-dimensional model shows at least four projecting arms, arranged radially near the presumed interface with the 30S subunit. The projecting arms are positioned around a cleft, which turns into a tunnel with a length of 100 to 120 angstroms and a diameter of up to 25 angstroms. This tunnel spans the particle and may provide the path taken by the nascent polypeptide chain.