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<jats:p>According to the commonly accepted view, David Hilbert completed the general theory of relativity at least 5 days before Albert Einstein submitted his conclusive paper on this theory on 25 November 1915. Hilbert's article, bearing the date of submission 20 November 1915 but published only on 31 March 1916, presents a generally covariant theory of gravitation, including field equations essentially equivalent to those in Einstein's paper. A close analysis of archival material reveals that Hilbert did not anticipate Einstein. The first set of proofs of Hilbert's paper shows that the theory he originally submitted is not generally covariant and does not include the explicit form of the field equations of general relativity.</jats:p>

<jats:p>Geomorphic evidence that Mars was warm enough to support flowing water about 3.8 billion years ago presents a continuing enigma that cannot be explained by conventional greenhouse warming mechanisms. Model calculations show that the surface of early Mars could have been warmed through a scattering variant of the greenhouse effect, resulting from the ability of the carbon dioxide ice clouds to reflect the outgoing thermal radiation back to the surface. This process could also explain how Earth avoided an early irreversible glaciation and could extend the size of the habitable zone on extrasolar planets around stars.</jats:p>

<jats:p> The generation of the green line of atomic oxygen by dissociative recombination of O <jats:sub>2</jats:sub> <jats:sup>+</jats:sup> occurs by the capture of an electron into a repulsive state of O <jats:sub>2</jats:sub> followed by dissociation along another state of a different electronic symmetry. The two states are coupled together by mixed symmetry Rydberg states. Quantum chemical calculations give a rate coefficient at room temperature of (0.39 <jats:sub>−0.19</jats:sub> <jats:sup>+0.31</jats:sup> ) × 10 <jats:sup>−8</jats:sup> cubic centimeters per second. The quantum yield of excited oxygen is within the range deduced from ground, rocket, and satellite observations. The rate coefficients and yields are needed in models of the optical emission, chemistry, and energy balance of planetary ionospheres. </jats:p>

<jats:p> Fluids associated with the San Andreas and companion faults in central and south-central California have high <jats:sup>3</jats:sup> He/ <jats:sup>4</jats:sup> He ratios. The lack of correlation between helium isotopes and fluid chemistry or local geology requires that fluids enter the fault system from the mantle. Mantle fluids passing through the ductile lower crust must enter the brittle fault zone at or near lithostatic pressures; estimates of fluid flux based on helium isotopes suggest that they may thus contribute directly to fault-weakening high-fluid pressures at seismogenic depths. </jats:p>

<jats:p>Because of the proximity of the Euler poles of rotation of the Pacific and Antarctic plates, small variations in plate kinematics are fully recorded in the axial morphology and in the geometry of the Pacific-Antarctic Ridge south of the Udintsev fracture zone. Swath bathymetry and magnetic data show that clockwise rotations of the relative motion between the Pacific and Antarctic plates over the last 6 million years resulted in rift propagation or in the linkage of ridge segments, with transitions from transform faults to giant overlapping spreading centers. This bimodal axial rearrangement has propagated southward for the last 30 to 35 million years, leaving trails on the sea floor along a 1000-kilometer-long V-shaped structure south of the Udintsev fracture zone.</jats:p>

<jats:p>The time it takes seismic waves to propagate from South Atlantic earthquakes through the inner core to station COL in Alaska has decreased systematically over the past 30 years. Travel times from three earthquakes in 1991 to an array of 37 seismometers in Alaska suggest that lateral gradients in seismic wavespeeds are steep in this part of the inner core. This combination of observations can be explained by postulating that the inner core is rotating 0.2° to 0.3° per year faster than the mantle.</jats:p>

<jats:p>The signal transduction pathway or pathways linking extracellular signals to myogenesis are poorly defined. Upon mitogen withdrawal from C2C12 myoblasts, the mitogen-activated protein kinase (MAPK) p42Erk2 is inactivated concomitant with up-regulation of muscle-specific genes. Overexpression of MAPK phosphatase-1 (MKP-1) inhibited p42Erk2 activity and was sufficient to relieve the inhibitory effects of mitogens on muscle-specific gene expression. Later during myogenesis, endogenous expression of MKP-1 decreased. MKP-1 overexpression during differentiation prevented myotube formation despite appropriate expression of myosin heavy chain. This indicates that muscle-specific gene expression is necessary but not sufficient to commit differentiated myocytes to myotubes and suggests a function for the MAPKs during the early and late stages of skeletal muscle differentiation.</jats:p>

<jats:p>In evaluating current combination drug regimens for treatment of human immunodeficiency virus (HIV) disease, it is important to determine the existence of viral reservoirs. After depletion of CD8 cells from the peripheral blood mononuclear cells (PBMCs) of both patients and normal donors, activation of patient CD4 lymphocytes with immobilized antibodies to CD3 and CD28 enabled the isolation of virus from PBMCs of six patients despite the suppression of their plasma HIV RNA to fewer than 50 copies per milliliter for up to 2 years. Partial sequencing of HIV pol revealed no new drug resistance mutations or discernible evolution, providing evidence for viral latency rather than drug failure.</jats:p>

<jats:p> The hypothesis that quiescent CD4 <jats:sup>+</jats:sup> T lymphocytes carrying proviral DNA provide a reservoir for human immunodeficiency virus–type 1 (HIV-1) in patients on highly active antiretroviral therapy (HAART) was examined. In a study of 22 patients successfully treated with HAART for up to 30 months, replication-competent virus was routinely recovered from resting CD4 <jats:sup>+</jats:sup> T lymphocytes. The frequency of resting CD4 <jats:sup>+</jats:sup> T cells harboring latent HIV-1 was low, 0.2 to 16.4 per 10 <jats:sup>6</jats:sup> cells, and, in cross-sectional analysis, did not decrease with increasing time on therapy. The recovered viruses generally did not show mutations associated with resistance to the relevant antiretroviral drugs. This reservoir of nonevolving latent virus in resting CD4 <jats:sup>+</jats:sup> T cells should be considered in deciding whether to terminate treatment in patients who respond to HAART. </jats:p>

<jats:p>Many neuropeptides and peptide hormones require amidation at the carboxyl terminus for activity. Peptidylglycine α-amidating monooxygenase (PAM) catalyzes the amidation of these diverse physiological regulators. The amino-terminal domain of the bifunctional PAM protein is a peptidylglycine α-hydroxylating monooxygenase (PHM) with two coppers that cycle through cupric and cuprous oxidation states. The anomalous signal of the endogenous coppers was used to determine the structure of the catalytic core of oxidized rat PHM with and without bound peptide substrate. These structures strongly suggest that the PHM reaction proceeds via activation of substrate by a copper-bound oxygen species. The mechanistic and structural insight gained from the PHM structures can be directly extended to dopamine β-monooxygenase.</jats:p>