Recalibrated Mariner 10 Color Mosaics: Implications for Mercurian Volcanism

Recalibration of Mariner 10 color image data allows the identification of distinct color units on the mercurian surface. We analyze these data in terms of opaque mineral abundance, iron content, and soil maturity and find color units consistent with the presence of volcanic deposits on Mercury's surface. Additionally, materials associated with some impact craters have been excavated from a layer interpreted to be deficient in opaque minerals within the crust, possibly analogous to the lunar anorthosite crust. These observations suggest that Mercury has undergone complex differentiation like the other terrestrial planets and the Earth's moon.     

Predictions of biodiversity response to genetically modified herbicide-tolerant crops

We simulated the effects of the introduction of genetically modified herbicide-tolerant (GMHT) crops on weed populations and the consequences for seed-eating birds. We predict that weed populations might be reduced to low levels or practically eradicated, depending on the exact form of management. Consequent effects on the local use of fields by birds might be severe, because such reductions represent a major loss of food resources. The regional impacts of GMHT crops are shown to depend on whether the adoption of GMHT crops by farmers covaries with current weed levels.     

Evidence for macromolecular protein rings in the absence of bulk water

We have examined the architecture of a protein complex in the absence of bulk water. By determining collision cross sections of assemblies of the trp RNA binding protein, TRAP, we established that the 11-membered ring topology of the complex can be maintained within a mass spectrometer. We also found that the binding of tryptophan enhances the stability of the ring structure and that addition of a specific RNA molecule increases the size of the complex and prevents structural collapse. These results provide definitive evidence that protein quaternary structure can be maintained in the absence of bulk water and highlight the potential of ion mobility separation for defining shapes of heterogeneous macromolecular assemblies.     

Vasopressin mRNA in the suprachiasmatic nuclei: daily regulation of polyadenylate tail length

Daily variation has been found in the length of the polyadenylate tail attached to vasopressin messenger RNA in the suprachiasmatic nuclei, which is the location of an endogenous circadian pacemaker in mammals. No such variation was found in the supraoptic or paraventricular nuclei. This variation in the length of the polyadenylate tail may underlie the circadian rhythm of vasopressin peptide levels in cerebrospinal fluid and is a unique example of a daily rhythm in messenger RNA structure.     

Clementine observations of the aristarchus region of the moon

Multispectral and topographic data acquired by the Clementine spacecraft provide information on the composition and geologic history of the Aristarchus region of the moon. Altimetry profiles show the Aristarchus plateau dipping about 1 degrees to the north-northwest and rising about 2 kilometers above the surrounding lavas of Oceanus Procellarum to the south. Dark, reddish pyroclastic glass covers the plateau to average depths of 10 to 30 meters, as determined from the estimated excavation depths of 100- to 1000-meter-diameter craters that have exposed materials below the pyroclastics. These craters and the walls of sinuous rilles also show that mare basalts underlie the pyroclastics across much of the plateau. Near-infrared images of Aristarchus crater reveal olivine-rich materials and two kilometer-sized outcrops of anorthosite in the central peaks. The anorthosite could be either a derivative of local magnesium-suite magmatism or a remnant of the ferroan anorthosite crust that formed over the primordial magma ocean.     

Volcanism on Mercury: evidence from the first MESSENGER flyby

The origin of plains on Mercury, whether by volcanic flooding or impact ejecta ponding, has been controversial since the Mariner 10 flybys (1974-75). High-resolution images (down to 150 meters per pixel) obtained during the first MESSENGER flyby show evidence for volcanic vents around the Caloris basin inner margin and demonstrate that plains were emplaced sequentially inside and adjacent to numerous large impact craters, to thicknesses in excess of several kilometers. Radial graben and a floor-fractured crater may indicate intrusive activity. These observations, coupled with additional evidence from color images and impact crater size-frequency distributions, support a volcanic origin for several regions of plains and substantiate the important role of volcanism in the geological history of Mercury.     

Structures of the CCR5 N terminus and of a tyrosine-sulfated antibody with HIV-1 gp120 and CD4

The CCR5 co-receptor binds to the HIV-1 gp120 envelope glycoprotein and facilitates HIV-1 entry into cells. Its N terminus is tyrosine-sulfated, as are many antibodies that react with the co-receptor binding site on gp120. We applied nuclear magnetic resonance and crystallographic techniques to analyze the structure of the CCR5 N terminus and that of the tyrosine-sulfated antibody 412d in complex with gp120 and CD4. The conformations of tyrosine-sulfated regions of CCR5 (alpha-helix) and 412d (extended loop) are surprisingly different. Nonetheless, a critical sulfotyrosine on CCR5 and on 412d induces similar structural rearrangements in gp120. These results now provide a framework for understanding HIV-1 interactions with the CCR5 N terminus during viral entry and define a conserved site on gp120, whose recognition of sulfotyrosine engenders posttranslational mimicry by the immune system.     

Atmospheric Effects of Pollutan: Pollutants which affect clouds are most likely to produce modifications in weather and climate

We have argued that aerosols are probably the principal agents by which pollutants may affect weather and climate. They are most likely to act by influencing the structure and distribution of clouds. On the local scale, the effects of pollutants on some aspects of weather are unmistakable. The effects of man-made pollutants on global climate are a matter of debate, but they may already be significant.