The origins of nuclear astrophysics at Caltech

Shortly before the start of World War II, several theoretical physicists, including Hans Bethe and Carl von Weizsacker, advanced the idea that the sun derives it energy from nuclear reactions within its core. C. C. Lauritsen and William Fowler, nuclear physicists at Caltech's Kellogg Laboratory, were among the first experimentalists to appreciate the application of nuclear physics to stellar interiors. Post-war strategies for studying nuclear processes in the stars included an innovative series of unofficial, weekly seminars with Mt. Wilson astronomers at director Ira Bowen's house, the testing of Bethe's carbon cycle in Kellogg, and the collaboration with a diverse group of scientists ranging from cosmologist Fred Hoyle to astronomers Margaret and Geoffrey Burbidge. The events leading up to the publication of the 1957 paper by Fowler, Hoyle, Burbidge, and Burbidge, in The Reviews of Modern Physics, now regarded as a watershed in the history of nuclear astrophysics, are discussed. For his work in low-energy nuclear astrophysics, Fowler won the 1983 Nobel Prize in physics

Role of the Putative Zinc Finger Domain of Saccharomyces cerevisiae DNA Polymerase epsilon in DNA Replication and the S/M Checkpoint Pathway

It has been proposed that C-terminal motifs of the catalytic subunit of budding yeast polymerase (pol) epsilon (POL2) couple DNA replication to the S/M checkpoint (Navas, T. A., Zheng, Z., and Elledge, S. J. (1995) Cell 80, 29-39). Scanning deletion analysis of the C terminus reveals that 20 amino acid residues between two putative C-terminal zinc fingers are essential for DNA replication and for an intact S/M cell cycle checkpoint. All mutations affecting the inter-zinc finger amino acids or the zinc fingers themselves are sensitive to methylmethane sulfonate and have reduced ability to induce RNR3, showing that the mutants are defective in the transcriptional response to DNA damage as well as the cell cycle response. The mutations affect the assembly of the pol epsilon holoenzyme. Two-hybrid assays show that the POL2 subunit interacts with itself, and that the replication and checkpoint mutants are specifically defective in the interaction, suggesting (but not proving) that direct or indirect dimerization may be important for the normal functions of pol epsilon . The POL2 C terminus is sufficient for interaction with DPB2, the essential and phylogenetically conserved subunit of pol epsilon , but not for interaction with DPB3. Neither Dpb3p nor Dpb2p homodimerizes in the two-hybrid assay

Analysis of the Essential Functions of the C-terminal Protein/Protein Interaction Domain of Saccharomyces cerevisiae pol epsilon and Its Unexpected Ability to Support Growth in the Absence of the DNA Polymerase Domain

As first observed by Wittenberg (Kesti, T., Flick, K., Keranen, S., Syvaoja, J. E., and Wittenburg, C. (1999) Mol. Cell 3, 679-685), we find that deletion mutants lacking the entire N-terminal DNA polymerase domain of yeast pol epsilon are viable. However, we now show that point mutations in DNA polymerase catalytic residues of pol epsilon are lethal. Taken together, the phenotypes of the deletion and the point mutants suggest that the polymerase of pol epsilon may normally participate in DNA replication but that another polymerase can substitute in its complete absence. Substitution is inefficient because the deletion mutants have serious defects in DNA replication. This observation raises the question of what is the essential function of the C-terminal half of pol epsilon . We show that the ability of the C-terminal half of the polymerase to support growth is disrupted by mutations in the cysteine-rich region, which disrupts both dimerization of the POL2 gene product and interaction with the essential DPB2 subunit, suggesting that this region plays an important architectural role at the replication fork even in the absence of the polymerase function. Finally, the S phase checkpoint, with respect to both induction of RNR3 transcription and cell cycle arrest, is intact in cells where replication is supported only by the C-terminal half of pol epsilon , but it is disrupted in mutants affecting the cysteine-rich region, suggesting that this domain directly affects the checkpoint rather than acting through the N-terminal polymerase active site

DNA polymerases required for repair of UV-induced damage in Saccharomyces cerevisiae

The ability of yeast DNA polymerase mutant strains to carry out repair synthesis after UV irradiation was studied by analysis of postirradiation molecular weight changes in cellular DNA. Neither DNA polymerase alpha, delta, epsilon, nor Rev3 single mutants evidenced a defect in repair. A mutant defective in all four of these DNA polymerases, however, showed accumulation of single-strand breaks, indicating defective repair. Pairwise combination of polymerase mutations revealed a repair defect only in DNA polymerase delta and epsilon double mutants. The extent of repair in the double mutant was no greater than that in the quadruple mutant, suggesting that DNA polymerases alpha and Rev3p play very minor, if any, roles. Taken together, the data suggest that DNA polymerases delta and epsilon are both potentially able to perform repair synthesis and that in the absence of one, the other can efficiently substitute. Thus, two of the DNA polymerases involved in DNA replication are also involved in DNA repair, adding to the accumulating evidence that the two processes are coupled

Negotiate or Litigate? Effects of WTO Judicial Delegation on U.S. Trade Politics

Goldstein and Steinberg argue that the World Trade Organization Appellate Body has been able to use its authority to engage in judicial lawmaking to reduce trade barriers in ways that would not otherwise have been possible through negotiation. This lawmaking authority was not the result of a purposeful delegation; rather, it was an unintended byproduct of the creation of an underspecified set of rules and procedures. There is nevertheless a high rate of compliance with Appellate Body decisions because decentralized enforcement can induce domestic importers to lobby for trade liberalization. In the US, this judicial lawmaking may also allow the President to achieve trade policies that are more liberal than those desired by Congress, if compliance can be achieved by a regulatory change or by sole Executive action

PROPERTY TAX AND TAX REFORM IN TEXAS: AN EQUITY CONCERN

The Governor of Texas has proposed a tax reform that lowers property tax and eliminates the franchise tax. The lost revenues are replaced by raising the sales tax and instituting a modified value-added tax. The issues are not unique to Texas, many states are considering tax issues. The current tax system is based on an economy that no longer exists and is not providing sufficient revenues. Given the changed economy of the state, modification of the tax system is reasonable. But the proposal increases regressive taxes and decreases the only progressive tax in the system. Overall the proposal is more regressive than the existing tax system.Agricultural and Food Policy,

Water/rock interactions in experimentally simulated dirty snowball and dirty iceball cometary nuclei

In the dirty snowball model for cometary nuclei, comet-nucleus materials are regarded as mixtures of volatile ices and relatively non-volatile minerals or chemical compounds. Carbonaceous chondrite meteorites are regarded as useful analogs for the rocky component. To help elucidate the possible physical geochemistry of cometary nuclei, preliminary results are reported of calorimetric experiments with two-component systems involving carbonaceous chondrites and water ice. Based on collective knowledge of the physics of water ice, three general types of interactions can be expected between water and minerals at sub-freezing temperatures: (1) heterogeneous nucleation of ice by insoluble minerals; (2) adsorption of water vapor by hygroscopic phases; and (3) freezing- and melting-point depression of liquid water sustained by soluble minerals. The relative and absolute magnitude of all three effects are expected to vary with mineral composition