Nucleotide control of interdomain interactions in the conformational reaction cycle of SecA

The SecA adenosine triphosphatase (ATPase) mediates extrusion of the amino termini of secreted proteins from the eubacterial cytosol based on cycles of reversible binding to the SecYEG translocon. We have determined the crystal structure of SecA with and without magnesium-adenosine diphosphate bound to the high-affinity ATPase site at 3.0 and 2.7 angstrom resolution, respectively. Candidate sites for preprotein binding are located on a surface containing the SecA epitopes exposed to the periplasm upon binding to SecYEG and are thus positioned to deliver preprotein to SecYEG. Comparisons with structurally related ATPases, including superfamily I and II ATP-dependent helicases, suggest that the interaction geometry of the tandem motor domains in SecA is modulated by nucleotide binding, which is shown by fluorescence anisotropy experiments to reverse an endothermic domain-dissociation reaction hypothesized to gate binding to SecYEG.     

Direct measurements of the convective recycling of the upper troposphere

We present a statistical representation of the aggregate effects of deep convection on the chemistry and dynamics of the upper troposphere (UT) based on direct aircraft observations of the chemical composition of the UT over the eastern United States and Canada during summer. These measurements provide unique observational constraints on the chemistry occurring downwind of convection and the rate at which air in the UT is recycled. These results provide quantitative measures that can be used to evaluate global climate and chemistry models.     

A 5-micron-bright spot on Titan: evidence for surface diversity

Observations from the Cassini Visual and Infrared Mapping Spectrometer show an anomalously bright spot on Titan located at 80 degrees W and 20 degrees S. This area is bright in reflected light at all observed wavelengths, but is most noticeable at 5 microns. The spot is associated with a surface albedo feature identified in images taken by the Cassini Imaging Science Subsystem. We discuss various hypotheses about the source of the spot, reaching the conclusion that the spot is probably due to variation in surface composition, perhaps associated with recent geophysical phenomena.     

Preliminary meteorological results on Mars from the viking 1 lander

The results from the meteorology instruments on the Viking 1 lander are presented for the first 4 sols of operation. The instruments are working satisfactorily. Temperatures fluctuated from a low of 188 degrees K to an estimated maximum of 244 degrees K. The mean pressure is 7.65 millibars with a diurnal variation of amplitude 0.1 millibar. Wind speeds averaged over several minutes have ranged from essentially calm to 9 meters per second. Wind directions have exhibited a remarkable regularity which may be associated with nocturnal downslope winds and gravitational oscillations, or to tidal effects of the diurnal pressure wave, or to both.     

Control of Gene Expression for the Genetic Engineering of Cereal Quality

The recent success of techniques for the direct transfer of individual genes to cereal species suggests that specific modifications to grain end-use properties will be achievable in the near future. The suitability of direct gene transfer to the problem, the choice of the promoter and transformation strategy need to be considered before attempting such modifications. This review discusses these questions with reference to current knowledge of seed-specific and, in particular, endosperm-specific and abscisic acid-responsive gene promoters. This perspective is of special importance in attempts to engineer cereal proteins.     

Ramifications of crop residue loading for soil microbial community composition,activity and nutrient supply

Variable results have been reported on the effects of crop residue loads on soil microbial properties. We investigated changes in soil bacterial composition, β-glucosidase enzyme activity and nutrient bioavailability in response to wheat residue loading. The treatments included three levels of above-ground wheat residues (removed, retained or supplemented), with or without fertilizer N. Bacteroidetes, Firmicutes and Verrucomicrobia (the first two are copiotrophs) were less abundant where residues were removed than where residues were retained or supplemented, but the reverse was true for Actinobacteria, Cyanobacteria, Chloroflexi and Nitrospirae (all oligotrophs, although some Actinobacteria can be copiotrophic). Actinobacteria were also less abundant where fertilizer N was applied, and the abundances of their genera (including Arthrobacter and Mycobacterium) increased where residues were removed, confirming that they were oligotrophic in this study. β-diversity showed similar differences in the bacterial community structures because of residue management, but α-diversity was not affected by residue management or N fertilizer. β-glucosidase enzyme activities increased as C inputs increased with residue manipulation and N fertilizer. The enzyme activities increased with increasing residue loading in the 0–15 cm soil depth, but decreased with soil depth. Soil K supply increased with increasing residue loading, but nitrate-N supply was highest with residue retention. These results demonstrate remarkable resilience of soil microbial functioning under a wide range of crop residue inputs, without adverse effects on enzyme activity attributable to inorganic N fertilizer. The increasing β-glucosidase activity with increasing residue loading probably explains why crop residue return does not always increase soil C stocks.     

Effects of in vitro lactoferricin and lactoferrin on the head kidney cells of European sea bass (Dicentrarchus labrax, L.)

Antimicrobial, anti-inflammatory and immunomodulating properties of lactoferrin have been demonstrated in mammals and in fish. However, in vivo, lactoferrin is digested by gastric pepsin treatment into the N-terminal derived peptide named lactoferricin. This has been so far overlooked in fish in vitro studies. The aim of the present study was to assess in vitro the effects of both lactoferricin and lactoferrin on the head kidney cells of European sea bass (Dicentrarchus labrax, L.) in order to determine their potential as dietary additives and to get some insight into their mode of action. In vitro lactoferricin decreased significantly the chemiluminescent response of head kidney cells but did not affect the zymosan-triggered chemiluminescence activity. On the other hand, a high concentration of lactoferrin directly stimulated chemiluminescence but reduced the zymosan-triggered chemiluminescence. The bactericidal activity of head kidney cells was also significantly diminished by pre-incubation with lactoferrin in a dose-dependent manner. Although no significant effect of lactoferricin or lactoferrin was evidenced on head kidney cellular viability, absent or negative effect on the priming of respiratory burst activity suggested that care should be taken when using lactoferrin in the diet of sea bass and high doses should be avoided. Hypotheses about the mechanisms of action of lactoferricin and lactoferrin are presented.     

Serum Cardiac Troponin I Concentrations in Cattle with Cardiac and Noncardiac Disorders

Background: Making a clinical diagnosis of pericarditis in cattle is difficult and additional diagnostic tests are needed to evaluate cattle with suspected pericarditis. Serum cardiac troponin I (cTnI) concentrations are increased in cattle with pericarditis, but the utility of measuring serum cTnI concentrations in cattle with suspected pericarditis in cattle remains unclear.
Objectives: To determine if serum cTnI concentrations in cattle can be used to differentiate pericarditis from other cardiac disorders and noncardiac thoracic diseases.
Animals: Seventy-seven clinically diseased cattle and 19 healthy control cattle.
Methods: Serum cTnI concentrations were measured using an Immunlite Troponin I immunometric chemiluminescent assay in consecutive cases of postmortem-confirmed pericarditis (n = 18), endocarditis (n = 15), chronic suppurative pneumonia (n = 13), congenital heart disease (n = 10), reticulitis (n = 3), mediastinal abscess (n = 7), thymic lymphoma (n = 6), and caudal vena cava thrombosis (n = 5). Serum cTnI concentrations were measured in 19 healthy cattle.
Results: Although serum cTnI concentrations were significantly higher in cattle with pericarditis compared with healthy cattle, they were not significantly different from concentrations in cattle with endocarditis, congenital cardiac disease, mediastinal abscess, reticulitis, caudal vena cava thrombosis, or chronic suppurative pneumonia.
Conclusions: Serum cTnI cannot be used to distinguish cattle with pericarditis from cattle with other primary cardiac diseases. In addition, serum cTnI concentrations cannot distinguish between cattle with primary cardiac diseases and those with other noncardiac, intrathoracic disorders.