To elucidate the mechanism of ␣A-crystallin chaperone function, a detailed thermodynamic analysis of its binding to destabilized, site-directed mutants of T4 lysozyme was carried out. The selected mutants form a ladder of stabilities spanning the 5-10 kcal/mol range of free energy of unfolding. The crystal structures of the majority of the mutants have been previously determined and found to be similar to that of the wild type with no evidence of static local unfolding. Complex formation between ␣A-crystallin and T4 lysozyme was observed directly via the changes in the electron paramagnetic resonance lineshape of a nitroxide introduced at a non-destabilizing, solvent exposed site in T4 lysozyme. ␣A-Crystallin differentially interacts with the mutants, binding the more destabilized ones to a larger extent despite the similar structure of their native states. Our results suggest that the states recognized by ␣A-crystallin are non-native excited states distinct from the unfolded state. Stable complexes are formed when the free energy of binding to ␣A-crystallin is on the order of the free energy associated with the transition from the excited state to the native state. Biphasic binding isotherms reveal two modes of interactions with distinct affinities and stoichiometries. Highly destabilized mutants preferentially bind to the high capacity mode, suggesting conformational preference in the use of each mode. Furthermore, binding can be enhanced by increased temperature and pH, which may be reflecting conformational changes in ␣A-crystallin oligomeric structure.In the crowded molecular environment of the cell, protein folding, stability, and solubility are critically dependent on a specialized protein machinery consisting of multiple superfamilies of heat shock proteins, the molecular chaperones. By recognizing and binding non-native protein states, chaperones protect the cell from the toxic and pathogenic consequences of protein aggregation (1, 2). These non-native states are not only a byproduct of the folding process but are also populated through fluctuations in the native structure, the rate of which increases under extreme physicochemical conditions. The diversity of the molecular chaperones has been associated with distinct roles at different stages of the protein life cycle and in response to different cellular conditions (3).The small heat shock protein (sHSP) 1 superfamily consists of oligomeric proteins of 4 -40 subunits with a molecular mass of less than 40 kDa/subunit (4 -6). The exact role of the sHSP in the heat shock response is poorly understood, although they have been associated with a spectrum of functions under permissive temperatures (7-10). In humans, six sHSP have been identified in various tissues (6). The ␣-crystallins are the main protein component in the lens, where they play a critical role in establishing and maintaining its optical properties (11-13). It has been hypothesized that ␣-crystallin chaperone function prevents the early aggregation and precipitation of lens proteins. In non-l...

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Summary 1.Invasion by alien plant species represents a challenge to land managers throughout the world as they attempt to restore frequent fire-adapted ecosystems following decades of fire exclusion. In ponderosa pine Pinus ponderosa forests of western North America, the response of alien species to restoration treatments has not been well documented, particularly for alien species capable of altering environmental conditions (transformers). Understanding alien species dynamics is critical for developing treatments that accomplish restoration goals while minimizing alien invasion. 2. We used a replicated, randomized block experiment to compare the effects of an untreated control and thin-only, burn-only and thin-burn treatments on alien and transformer understorey species at multiple spatial scales (1 m 2 , 100 m 2 and 1000 m 2 ). Data were collected pre-treatment and for multiple post-treatment years. We compared richness and cover of alien species and transformer species among treatments, and identified environmental variables correlated with transformer species cover. Indicator species analysis was used to identify transformer species associated with specific treatments. 3. Alien and transformer species richness and cover were significantly higher in the thin-burn than in all other treatments at all spatial scales. Thin-only and burn-only treatments showed greater alien and transformer species responses than the control at the larger 100-m 2 and 1000-m 2 scales. 4. Increased transformer cover was strongly correlated with increased tree crown scorch height and removal of overstorey trees. 5. The thin-burn treatment had four transformer species as indicators, the thin-only had one, while the burn-only and control had none. 6. Synthesis and applications . The results show that alien species, including transformers, respond to restoration treatments, especially the combined thin-burn treatment. Therefore monitoring for alien species invasion is an essential component of a restoration programme. Abundance of transformer species increased with increasing disturbance intensity, suggesting that less intense single-disturbance treatments (burnonly, thin-only) or incremental treatments may be preferred in some applications. Where more intense treatments are required to meet management objectives, specific strategies, such as seeding of native species, limiting grazing before and after treatment and harvesting over a protective winter snowpack, may be necessary to limit alien invasion.

The loss of critical habitat provided by late successional forests has prompted the search for management options that can accelerate the development of late successional forest structure in young stands. We examined operational-scale commercial thinning treatments at seven sites to evaluate if thinning could accelerate development of late successional forest structures in 40-60 year old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests. Thinning treatments included an untreated control, high density, moderate density, and variable density retention. All thinning treatments had leave islands, and moderate density and variable density included harvest-created gaps. Thinned units, especially moderate density and variable density, had greater spatial variability in tree density, supported lower live branches, had greater tree regeneration and growth, and had slightly lower mortality relative to the control. Canopy gaps extended the range of stand densities and increased growth of trees immediately along gap edges. However, thinning had little effect on growth of the largest Douglas-fir trees and did little to provide large snags or coarse woody debris. These results suggest that thinning treatments can accelerate some aspects, e.g., spatial variability, of late successional forest structures. Other attributes, such as large trees and snags, may prove less responsive to thinning treatments, at least in the short term. Including tree retention levels lower than typical management applications and formation of canopy gaps provide the wide range of conditions that appears beneficial for developing late successional forest structure.Résumé : La perte d'habitats critiques associés aux forêts de fin de succession a encouragé la mise au point d'options d'aménagement qui peuvent accélérer le développement d'une structure forestière de fin de succession dans de jeunes peuplements. Nous avons étudié des traitements d'éclaircie commerciale à l'échelle opérationnelle effectués sur sept stations pour évaluer si l'éclaircie pouvait accélérer le développement de structures forestières de fin de succession dans des peuplements de douglas vert (Pseudotsuga menziesii (Mirb.) Franco) âgés de 40 à 60 ans. Les traitements d'éclaircie incluaient un témoin non traité et la rétention d'arbres à densité forte, à densité modérée et à densité variable. Tous les traitements d'éclaircie comportaient des îlots non traités et les traitements densité modérée et densité variable incluaient des trouées créées par la coupe. Comparativement aux témoins, les unités éclaircies, particulièrement les traitements densité modérée et densité variable, avaient une plus grande variabilité spatiale de la densité d'arbres, supportaient des branches vivantes plus basses, avaient plus de régénération, une meilleure croissance des arbres et légèrement moins de mortalité. Les trouées dans la canopée augmentaient l'étendue de la densité des peuplements et la croissance des arbres situés en bordure. Toutefois, les éclair-cies ont eu peu d'effet sur la croissan...

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Increasing fire severity and warmer, drier postfire conditions are making forests in the western United States (West) vulnerable to ecological transformation. Yet, the relative importance of and interactions between these drivers of forest change remain unresolved, particularly over upcoming decades. Here, we assess how the interactive impacts of changing climate and wildfire activity influenced conifer regeneration after 334 wildfires, using a dataset of postfire conifer regeneration from 10,230 field plots. Our findings highlight declining regeneration capacity across the West over the past four decades for the eight dominant conifer species studied. Postfire regeneration is sensitive to high-severity fire, which limits seed availability, and postfire climate, which influences seedling establishment. In the near-term, projected differences in recruitment probability between low- and high-severity fire scenarios were larger than projected climate change impacts for most species, suggesting that reductions in fire severity, and resultant impacts on seed availability, could partially offset expected climate-driven declines in postfire regeneration. Across 40 to 42% of the study area, we project postfire conifer regeneration to be likely following low-severity but not high-severity fire under future climate scenarios (2031 to 2050). However, increasingly warm, dry climate conditions are projected to eventually outweigh the influence of fire severity and seed availability. The percent of the study area considered unlikely to experience conifer regeneration, regardless of fire severity, increased from 5% in 1981 to 2000 to 26 to 31% by mid-century, highlighting a limited time window over which management actions that reduce fire severity may effectively support postfire conifer regeneration.