Intracellular targeting of a hordeiviral membrane-spanning movement protein: sequence requirements and involvement of an unconventional mechanism

The membrane-spanning protein TGBp3 is one of the three movement proteins (MPs) of Poa semilatent virus. TGBp3 is thought to direct other viral MPs and genomic RNA to peripheral bodies located in close proximity to plasmodesmata. We used the ectopic expression of green fluorescent protein-fused TGBp3 in epidermal cells of Nicotiana benthamiana leaves to study the TGBp3 intracellular trafficking pathway. Treatment with inhibitors was used to reveal that the targeting of TGBp3 to plasmodesmata does not require a functional cytoskeleton or secretory system. In addition, the suppression of endoplasmic reticulum-derived vesicle formation by a dominant negative mutant of small GTPase Sar1 had no detectable effect on TGBp3 trafficking to peripheral bodies. Collectively, these results suggested the involvement of an unconventional pathway in the intracellular transport of TGBp3. The determinants of targeting to plasmodesmata were localized to the C-terminal region of TGBp3, including the conserved hydrophilic and terminal membrane-spanning domains.     

A globin-coupled oxygen sensor from the facultatively alkaliphilic<Emphasis Type="Italic"> Bacillus halodurans</Emphasis> C-125

We have recently discovered heme-containing signal transducers from the archaeon Halobacterium salinarum (HemAT-Hs) and the gram-positive bacterium Bacillus subtilis (HemAT-Bs). These proteins bind diatomic oxygen and trigger aerotactic responses. We identified that HemAT oxygen-sensing domains contain a globin-coupled sensor (GCS) motif, which exists as a two-domain transducer, having no similarity to the PAS domain (Period circadian protein, Ah receptor nuclear translocator protein, Single-minded protein) superfamily transducers. Using the GCS motif, we predicted that a 439-amino-acid protein annotated as a methyl-accepting chemotaxis protein (MCP) in the facultatively alkaliphilic bacterium Bacillus halodurans is a globin-coupled oxygen sensor. We cloned, expressed, and purified GCS(Bh), and performed its spectral analysis. GCS(Bh), binds heme and shows myoglobin-like spectra. This suggests that GCS(Bh) acts as an oxygen sensor and transmits a conformational signal through a linked signaling domain to trigger an aerotactic response in B. halodurans.     

Linking the composition of bacterioplankton to rapid turnover of dissolved dimethylsulphoniopropionate in an algal bloom in the North Sea

The algal osmolyte, dimethylsulphoniopropionate (DMSP), is abundant in the surface oceans and is the major precursor of dimethyl sulphide (DMS), a gas involved in global climate regulation. Here, we report results from an in situ Lagrangian study that suggests a link between the microbially driven fluxes of dissolved DMSP (DMSPd) and specific members of the bacterioplankton community in a North Sea coccolithophore bloom. The bacterial population in the bloom was dominated by a single species related to the genus Roseobacter , which accounted for 24% of the bacterioplankton numbers and up to 50% of the biomass. The abundance of the Roseobacter cells showed significant paired correlation with DMSPd consumption and bacterioplankton production, whereas abundances of other bacteria did not. Consumed DMSPd (28 nM day⁻¹) contributed 95% of the sulphur and up to 15% of the carbon demand of the total bacterial populations, suggesting the importance of DMSP as a substrate for the Roseobacter -dominated bacterioplankton. In dominating DMSPd flux, the Roseobacter species may exert a major control on DMS production. DMSPd turnover rate was 10 times that of DMS (2.7 nM day⁻¹), indicating that DMSPd was probably the major source of DMS, but that most of the DMSPd was metabolized without DMS production. Our study suggests that single species of bacterioplankton may at times be important in metabolizing DMSP and regulating the generation of DMS in the sea.     

Expression of VirB2 protein-containing structures on Agrobacterium in mating cultures

Exocellular structures containing VirB2 proteins were, for the first time, localized on the surface of Agrobacterium by transmission electron microscopy. Using colloidal gold (CG)-labeled VirB2-specific antibodies, it was shown that VirB2 proteins enter into the composition of short surface pili, which emerge at the poles of acetosyringone (AS)-induced Agrobacterium cells. However, cells of the Ti plasmidless A. tumefaciens strain UBAPF-2 and cells not induced with AS were incapable of pilus synthesis. In suspension, mating Agrobacterium cells were connected together by short thick bridges. It was found that these bridges did not include as part of their structure CG-labeled VirB1 and VirB2 proteins. We did not find the tetracycline-resistant transconjugants after mating of A. tumefaciens donor cells harboring binary systems with plasmid-free A. tumefaciens GM-I 9023 in vir-induced and vir-uninduced conditions. However, the same strains can transfer pSUP106 plasmid via a vir-dependent way. We found that activated vir genes slightly stimulate pTd33 plasmid transfer via a tra-dependent pathway to plasmid-free strain UBAPF-2. It seems, that vir-induced T-DNA/plasmid DNA transfer machinery is not essential for the conjugation process between agrobacterial cells but may participate in this process.     

Barking foxes, Alopex lagopus: field experiments in individual recognition in a territorial mammal

During field studies on a wild population of Arctic foxes, Alopex lagopus, on the Commander Island Mednyi (Northern Pacific) we examined whether acoustic long-distance signals were used for individual recognition. Barks of 10 individually known animals from five neighbouring groups were tape recorded. The spectral characteristics of the barks were described in terms of averaged 1/12 octave spectra.With a discriminant function analysis, more than 90% of the calls could be assigned to the correct individual on the basis of the spectral parameters. Discrimination was only slightly improved when we added temporal parameters to the analysis. We carried out playback experiments with eight foxes near the territory boundary of their family groups. The foxes were significantly more likely to respond with territorial behaviour and longer barking bouts to playbacks of neighbours or strangers than to playbacks of group members. We conclude that individuals can distinguish between barks of members of their own social group and those of other foxes. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

No statistical support for correlation between the positions of protein interaction sites and alternatively spliced regions

Background  

Alternative splicing is an efficient mechanism for increasing the variety of functions fulfilled by proteins in a living cell. It has been previously demonstrated that alternatively spliced regions often comprise functionally important and conserved sequence motifs. The objective of this work was to test the hypothesis that alternative splicing is correlated with contact regions of protein-protein interactions.     

LDL receptor-related proteins 5 and 6 in Wnt/beta-catenin signaling: arrows point the way

Wnt signaling through the canonical beta-catenin pathway plays essential roles in development and disease. Low-density-lipoprotein receptor-related proteins 5 and 6 (Lrp5 and Lrp6) in vertebrates, and their Drosophila ortholog Arrow, are single-span transmembrane proteins that are indispensable for Wnt/beta-catenin signaling, and are likely to act as Wnt co-receptors. This review highlights recent progress and unresolved issues in understanding the function and regulation of Arrow/Lrp5/Lrp6 in Wnt signaling. We discuss Arrow/Lrp5/Lrp6 interactions with Wnt and the Frizzled family of Wnt receptors, and with the intracellular beta-catenin degradation apparatus. We also discuss the regulation of Lrp5/Lrp6 by other extracellular ligands, and LRP5 mutations associated with familial osteoporosis and other disorders.