Base-CP proteasome can serve as a platform for stepwise lid formation

26S proteasome, a major regulatory protease in eukaryotes, consists of a 20S proteolytic core particle (CP) capped by a 19S regulatory particle (RP). The 19S RP is divisible into base and lid sub-complexes. Even within the lid, subunits have been demarcated into two modules: module 1 (Rpn5, Rpn6, Rpn8, Rpn9 and Rpn11), which interacts with both CP and base sub-complexes and module 2 (Rpn3, Rpn7, Rpn12 and Rpn15) that is attached mainly to module 1. We now show that suppression of RPN11 expression halted lid assembly yet enabled the base and 20S CP to pre-assemble and form a base-CP. A key role for Regulatory particle non-ATPase 11 (Rpn11) in bridging lid module 1 and module 2 subunits together is inferred from observing defective proteasomes in rpn11–m1, a mutant expressing a truncated form of Rpn11 and displaying mitochondrial phenotypes. An incomplete lid made up of five module 1 subunits attached to base-CP was identified in proteasomes isolated from this mutant. Re-introducing the C-terminal portion of Rpn11 enabled recruitment of missing module 2 subunits. In vitro, module 1 was reconstituted stepwise, initiated by Rpn11–Rpn8 heterodimerization. Upon recruitment of Rpn6, the module 1 intermediate was competent to lock into base-CP and reconstitute an incomplete 26S proteasome. Thus, base-CP can serve as a platform for gradual incorporation of lid, along a proteasome assembly pathway. Identification of proteasome intermediates and reconstitution of minimal functional units should clarify aspects of the inner workings of this machine and how multiple catalytic processes are synchronized within the 26S proteasome holoenzymes.     

Can we predict butterfly diversity along an elevation gradient from space?

An important challenge in ecology is to predict patterns of biodiversity across eco‐geographical gradients. This is particularly relevant in areas that are inaccessible, but are of high research and conservation value, such as mountains. Potentially, remotely‐sensed vegetation indices derived from satellite images can help in predicting species diversity in vast and remote areas via their relationship with two of the major factors that are known to affect biodiversity: productivity and spatial heterogeneity in productivity. Here, we examined whether the Normalized Difference Vegetation Index (NDVI) can be used effectively to predict changes in butterfly richness, range size rarity and beta diversity along an elevation gradient. We examined the relationship between butterfly diversity and both the mean NDVI within elevation belts (a surrogate of productivity) and the variability in NDVI within and among elevation belts (surrogates for spatial heterogeneity in productivity). We calculated NDVI at three spatial extents, using a high spatial resolution QuickBird satellite image. We obtained data on butterfly richness, rarity and beta diversity by field sampling 100 m quadrats and transects between 500 and 2200 m in Mt Hermon, Israel. We found that the variability in NDVI, as measured both within and among adjacent elevation belts, was strongly and significantly correlated with butterfly richness. Butterfly range size rarity was strongly correlated with the mean and the standard deviation of NDVI within belts. In our system it appears that it is spatial heterogeneity in productivity rather than productivity per se that explained butterfly richness. These results suggest that remotely‐sensed data can provide a useful tool for assessing spatial patterns of butterfly richness in inaccessible areas. The results further indicate the importance of considering spatial heterogeneity in productivity along elevation gradients, which has no lesser importance than productivity in shaping richness and rarity, especially at the local scale.     

Novel terpenoids of the fungus Aspergillus insuetus isolated from the Mediterranean sponge Psammocinia sp. collected along the coast of Israel

Three novel meroterpenoids, insuetolides A-C (1-3) and four drimane sesquiterpenes, the new (E)-6-(4'-hydroxy-2'-butenoyl)-strobilactone A (4) and the known 2α, 9α, 11-trihydroxy-6-oxodrim-7-ene (5), strobilactone A (6) and (E,E)-6-(6',7'-dihydroxy-2',4'-octadienoyl)-strobilactone A (7), were isolated from the EtOAc extract of the culture medium of the marine-derived fungus Aspergillus insuetus (OY-207), which was isolated from the Mediterranean sponge Psammocinia sp. The structures of the compounds were determined by spectroscopic methods. Insuetolides A-C reveal a new carbon skeleton derived from the cyclization of farnesyl and 3, 5-dimethylorsellinic acid. Compounds 1, 6, and 7 exhibited anti-fungal activity towards Neurospora crassa with MIC values of 140, 242, and 162 μM, respectively; and compounds 3, 4, and 7 exhibited mild cytotoxicity towards MOLT-4 human leukemia cells.     

Reconstructing a puzzle: existence of cyanophages containing both photosystem‐I and photosystem‐II gene suites inferred from oceanic metagenomic datasets

Cyanobacteria play a key role in marine photosynthesis, which contributes to the global carbon cycle and to the world oxygen supply. Genes encoding the photosystem‐II (PSII) reaction centre are found in many cyanophage genomes, and it was suggested that the horizontal transfer of these genes might be involved in increasing phage fitness. Recently, evidence for the existence of phages carrying Photosystem‐I (PSI) genes was also reported. Here, using a combination of different marine metagenomic datasets and a unique crossing of the datasets, we now describe the finding of phages that, as in plants and cyanobacteria, contain both PSII and PSI genes. In addition, these phages also contain NADH dehydrogenase genes. The presence of modified PSII and PSI genes in the same viral entities in combination with electron transfer proteins like NAD(P)H dehydrogenase (NDH‐1) strongly points to a role in perturbation of the cyanobacterial host photosynthetic electron flow. We therefore suggest that, depending on the physiological condition of the infected cyanobacterial host, the viruses may use different options to maximize survival. The modified PSI may alternate between functioning with PSII in linear electron transfer and contributing to the production of both NADPH and ATP or functioning independently of PSII in cyclic mode via the NDH‐1 complex and thus producing only ATP.     

Is population growth conducive to the sustainability of cooperation?

This paper asks whether population growth is conducive to the sustainability of cooperation. A simple model is developed in which farmers who live around a circular lake engage in trade with their adjacent neighbors. The payoffs from this activity are governed by a prisoner's dilemma “rule of engagement.” Every farmer has one son when the population is not growing, or two sons when it is growing. In the former case, the son takes over the farm when his father dies. In the latter case, one son stays on his father's farm, whereas the other son settles around another lake, along with the “other” sons of the other farmers. During his childhood, each son observes the strategies and the payoffs of his father and of the trading partners of his father, and imitates the most successful strategy when starting farming on his own. Then mutant defectors are introduced into an all-cooperator community. The defector strategy may spread. A comparison is drawn between the impact in terms of the sustainability of cooperation of the appearance of the mutants in a population that is not growing, and in one that is growing. It is shown that the ex-ante probability of sustaining the cooperation strategy is higher for a community that is growing than for a stagnant community.     

Nuclear import of an intact preassembled proteasome particle

The 26S proteasome is a conserved 2.5 MDa protein degradation machine that localizes to different cellular compartments, including the nucleus. Little is known about the specific targeting mechanisms of proteasomes in eukaryotic cells. We used a cell-free nuclear reconstitution system to test for nuclear targeting and import of distinct proteasome species. Three types of stable, proteolytically active proteasomes particles were purified from Xenopus egg cytosol. Two of these, the 26S holoenzyme and the 20S core particle, were targeted to the nuclear periphery but did not reach the nucleoplasm. This targeting depends on the presence of mature nuclear pore complexes (NPCs) in the nuclear envelope. A third, novel form, designated here as 20S+, was actively imported through NPCs. The 20S+ proteasome particle resembles recently described structural intermediates from other systems. Nuclear import of this particle requires functional NPCs, but it is not directly regulated by the Ran GTPase cycle. The mere presence of the associated "+" factors is sufficient to reconstitute nuclear targeting and confer onto isolated 20S core particles the ability to be imported. Stable 20S+ particles found in unfertilized eggs may provide a means for quick mobilization of existing proteasome particles into newly formed nuclear compartments during early development.     

Dual function of Rpn5 in two PCI complexes, the 26S proteasome and COP9 signalosome

Subunit composition and architectural structure of the 26S proteasome lid is strictly conserved between all eukaryotes. This eight-subunit complex bears high similarity to the eukaryotic translation initiation factor 3 and to the COP9 signalosome (CSN), which together define the proteasome CSN/COP9/initiation factor (PCI) troika. In some unicellular eukaryotes, the latter two complexes lack key subunits, encouraging questions about the conservation of their structural design. Here we demonstrate that, in Saccharomyces cerevisiae, Rpn5 plays dual roles by stabilizing proteasome and CSN structures independently. Proteasome and CSN complexes are easily dissected, with Rpn5 the only subunit in common. Together with Rpn5, we identified a total of six bona fide subunits at roughly stoichiometric ratios in isolated, affinity-purified CSN. Moreover, the copy of Rpn5 associated with the CSN is required for enzymatic hydrolysis of Rub1/Nedd8 conjugated to cullins. We propose that multitasking by a single subunit, Rpn5 in this case, allows it to function in different complexes simultaneously. These observations demonstrate that functional substitution of subunits by paralogues is feasible, implying that the canonical composition of the three PCI complexes in S. cerevisiae is more robust than hitherto appreciated.     

Architecture and development of the Neurospora crassa hypha -- a model cell for polarized growth

Neurospora crassa has been at the forefront of biological research from the early days of biochemical genetics to current progress being made in understanding gene and genetic network function. Here, we discuss recent developments in analysis of the fundamental form of fungal growth, development and proliferation -- the hypha. Understanding the establishment and maintenance of polarity, hyphal elongation, septation, branching and differentiation are at the core of current research. The advances in the identification and functional dissection of regulatory as well as structural components of the hypha provide an expanding basis for elucidation of fundamental attributes of the fungal cell. The availability and continuous development of various molecular and microscopic tools, as utilized by an active and co-supportive research community, promises to yield additional important new discoveries on the biology of fungi.