Hsp70 in mitochondrial biogenesis

The family of hsp70 (70 kilodalton heat shock protein) molecular chaperones plays an essential and diverse role in cellular physiology, Hsp70 proteins appear to elicit their effects by interacting with polypeptides that present domains which exhibit non-native conformations at distinct stages during their life in the cell. In this paper we review work pertaining to the functions of hsp70 proteins in chaperoning mitochondrial protein biogenesis. Hsp70 proteins function in protein synthesis, protein translocation across mitochondrial membranes, protein folding and finally the delivery of misfolded proteins to proteolytic enzymes in the mitochondrial matrix

Substituting root numbers for length: improving the use of minirhizotrons to study fine root dynamics

Minirhizotrons provide a unique way to repeatedly measure the production and fate of individual root segments, while minimizing soil disturbance and the confounding of spatial-temporal variation. However, the time associated with processing videotaped minirhizotron images limits the amount of data that can be extracted in a reasonable amount of time. We found that this limitation can be minimized using a more easily measured variable r (i.e. root numbers) as a substitute of root length. Linear regression models were fitted between root length versus root number for production and mortality of seven sample datasets of varying tree species and treatments. The resulting r2 values ranged from 0.79 to 0.99, suggesting that changes in root numbers can be used to predict root length dynamics reliably. Slope values, representing the mean root segment length (MRSL), ranged from 2.34 to 8.38 mm per root segment for both production and mortality. Most treatments did not alter MRSL substantially, the exceptions being CO2 treatments and a girdling treatment that altered plant community composition and, consequently, root morphology. The high r2 values demonstrated arobust relationship between variables irrespective of species or treatments. Once the quantitative relationship between root lengths and numbers has been established for a particular species-treatment combination, quantifying changes in root number through time should substantially decrease the time required to quantify root dynamics. © 2003 Elsevier Science B.V. All rights reserved

Improved spectral fitting of nitrogen dioxide from OMI in the 405–465 nm window

An improved nitrogen dioxide (NO2) slant column density retrieval for the Ozone Monitoring Instrument (OMI) in the 405–465 nm spectral region is presented. Since the launch of OMI on board NASA's EOS-Aura satellite in 2004, differential optical absorption spectroscopy (DOAS) retrievals of NO2 slant column densities have been the starting point for the KNMI DOMINO and NASA SP NO2 vertical column data as well as the OMI NO2 data of some other institutes. However, recent intercomparisons between NO2 retrievals from OMI and other UV/Vis and limb spectrometers, as well as ground-based measurements, suggest that OMI stratospheric NO2 is biased high. This study revises and, for the first time, fully documents the OMI NO2 retrieval in detail. The representation of the OMI slit function to convolve high-resolution reference spectra onto the relevant spectral grid is improved. The window used for the wavelength calibration is optimised, leading to much-reduced fitting errors. Ozone and water vapour spectra used in the fit are updated, reflecting the recently improved knowledge of their absorption cross section in the literature. The improved spectral fit also accounts for absorption by the O2–O2 collision complex and by liquid water over clear-water areas. The main changes in the improved spectral fitting result from the updates related to the wavelength calibration: the RMS error of the fit is reduced by 23% and the NO2 slant column by 0.85 × 1015 molec cm-2, independent of latitude, solar zenith angle and NO2 value. Including O2–O2 and liquid water absorption and updating the O3 and water vapour cross-section spectra further reduces NO2 slant columns on average by 0.35 × 1015 molec cm-2, accompanied by a further 9% reduction in the RMS error of the fit. The improved OMI NO2 slant columns are consistent with independent NO2 retrievals from other instruments to within a range that can be explained by photochemically driven diurnal increases in stratospheric NO2 and by small differences in fitting window and approach. The revisions indicate that current OMI NO2 slant columns suffered mostly from an additive positive offset, which is removed by the improved wavelength calibration and representation of the OMI slit function. It is therefore anticipated that the improved NO2 slant columns are most important to retrievals of spatially homogeneous stratospheric NO2 rather than to heterogeneous tropospheric NO2

Mapping the decision to quit : a refinement and test of the unfolding model of voluntary turnover

We report a test of an influential theory of employee turnover: the unfolding model (Lee & Mitchell, 1994; Lee, Mitchell, Holtom, McDaniel, & Hill, 1999). We describe and critique this classificatory model, and propose both theory-based and empirical refinements. The two extant tests of the current version of the model have both been with accountants in the United States, so the generalisability of the model is as yet unproven. We present results of an attempt to classify 352 nurse leavers from the United Kingdom's National Health Service using the unfolding model. In contrast to the findings of Lee et al. (1999), the model failed to classify a substantial number of nurse leavers, and specific hypotheses derived from the model received only partial support. Classification failures were investigated using both quantitative and qualitative data. Leavers were more likely to be classified if they had no dependants and described their quit as avoidable. Although the unfolding model incorporates more kinds of turnover than traditional turnover models, such systematic classification failure casts doubt on claims that it offers a comprehensive account of turnover. We explain failures with reference to: (i) shortcomings in a key measure; (ii) the characteristics of the occupational group studied; and (iii) the extremely tight labor market for this group of leavers

A global stratospheric bromine monoxide climatology based on the BASCOE chemical transport model

A new climatology of stratospheric BrO profiles based on a parameterization using dynamical and chemical indicators has been developed, with the aim to apply it to the retrieval of tropospheric BrO columns from space nadir measurements. The adopted parameterization is based on three years of output data from the 3-D chemistry transport model BASCOE. The impact of the atmospheric dynamics on the stratospheric BrO distribution is treated by means of Br-y/ozone correlations built from 3-D-CTM model results, while photochemical effects are taken into account using stratospheric NO2 columns as an indicator of the BrO/Br-y ratio. The model simulations have been optimized for bromine chemistry and budget, and validated through comparisons using an extensive data set of ground-based, balloon-borne and satellite limb (SCIAMACHY) stratospheric BrO observations