Precursor Backbone Research Articles

How does the precursor backbone length affect the grafting efficiency and kinetics for bottlebrush polystyrenes prepared by graft-onto Strategy?

The clarification of the potential dependence of grafting efficiency on the backbone length during the graft-onto reaction process is extremely important for subsequent structure–property study. In this work, by using alkyne-functional polypropargyne acrylate (PPANb, Mw/Mn < 1.10 and Nb = 960, 193, 35) and azide-functional polystyrene (PSNs, Mw/Mn < 1.15 and Ns = 54, 38, 22) as the backbone and sidechain precursors, we have investigated the Nb-dependence of the grafting reaction during the graft-onto click process. Specifically, the influence of solution concentration and feed ratio are investigated, and a combination of SEC characterization, Gaussian fitting and theoretical analysis is used to estimate the Nb-dependent grafting reaction for the bottlebrush product (PPANb-g-PSNs). The main findings include: 1) when the reaction time (t) is sufficient long (t = 24 h), the grafting efficiency is found to be nearly irrelevant with Nb, even if we consider 2 ∼ 5 times of difference in the diffusion coefficient (D) based the well-known scaling relation of D ∼ Nb1/2 in the semidilute reaction solution; 2) the time-dependent kinetics investigation further shows abnormal and different pathways for different backbone lengths when 0 min < t < 10 min, but the final grafting efficiency determined at t = 300 min shows no much difference, going back to the preliminary result of equilibrium state at t = 24 h; 3) the origin of abnormal pathways may be attributed to the relatively poor signal-to-noise ratio and potential dependence of dn/dC of PPANb-g-PSNs product on the composition at low grafting density range, which needs clarification in future. For the first time, our result has unambiguously demonstrated that, for a mixed solution of reaction system composed of backbone precursors with their lengths differing by hundreds of times, the polydispersity effect of the backbone length does not affect the final grafting efficiency during the process, no matter for long or short sidechain grafts. The result implies that it is the local dynamics of chain segments, instead of the overall translational diffusion dominates the graft-onto process in the concentration-regime studied.

Polyamide-imide copolymer-derived carbon molecular sieve membranes for efficient hydrogen/carbon dioxide separation

Carbon molecular sieve (CMS) membranes are emerging porous carbon membranes for chemical separation and purification. Polyamide-imide (PAI) copolymers have shown attractive separation performance for natural gas upgrading and organic solvent separations. However, PAIs are rarely used as precursors to derive CMS membranes. This work shows that CMS hollow fiber membranes made from a PAI (Torlon®) can provide highly competitive H2 permeability and H2/CO2 selectivity overcoming the 2008 Robeson upper bound under both single-gas and mixed-gas permeation. With imide and amide moieties, the PAI showed intermediate H2/CO2 separation performance between a polyimide (PI) and a polyaramid (PA). Interestingly, the trend was translated to the CMS membranes, i.e., the PAI-derived CMS membrane showed intermediate H2/CO2 separation performance between the PI-derived CMS membrane and PA-derived CMS membrane with an excellent balance of H2 permeability and H2/CO2 selectivity. Sorption studies indicate that the PAI-derived CMS membrane had intermediate H2 diffusivity and H2/CO2 diffusion selectivity, which was further attributed to its intermediate ultramicropore size. To our best knowledge, this was the first report of PAI-derived CMS hollow fiber membranes with competitive gas separation performance and the first investigation of the chemistry and pore structure of PAI-derived porous carbon. This study also underscores the role of precursor backbone chemistry in tailoring CMS membrane properties, further suggesting that CMS membranes derived from copolymers comprising mixed backbone chemistry can give simultaneously attractive permeability and selectivity.

One-Pot Enzymatic Synthesis of Heparin from N-Sulfoheparosan.

Heparin, a glycosaminoglycan-based anticoagulant drug, is prepared as an extract of animal tissues. Heparosan, an Escherichia coli (E. coli) K5 capsular polysaccharide with the structure →4)-β-D-glucuronic acid (1→4)-β-D-N-acetylglucosamine (1→, corresponds to the precursor backbone in the Golgi-based biosynthesis of heparin. Anticoagulant heparin is prepared in a one-pot synthesis using a chemically prepared derivative of heparosan called N-sulfoheparosan (NSH), recombinant Golgi enzymes expressed in E. coli, and the 3-phosphoadenosine-5-phosphosulfate (PAPS) cofactor.

Enzyme-instructed supramolecular assemblies promote intracellular boron accumulation for boron neutron capture therapy

Selective accumulation of boron agents in cancer cells is of critical importance for BNCT. Here we involve enzyme-instructed supramolecular assembly (EISA) to facilitate the accumulation of a typical boron agent borylphenylalanine (BPA) in cancer cells. By covalently conjugating BPA to the phosphorylated assembly precursor, the boron-bearing precursors undergo phosphatase-catalyzed dephosphorylation to yield assembly molecules, which then self-assemble to form nanomaterials. Due to the up-regulated phosphatase activity of cancer cells, kinetic preference allows the EISA to accumulate boron in HeLa cells selectively. Interestingly, by attaching BPA on the backbone or side-chain of precursor, the boron-bearing isomers show different assembly propensity with time-dependent morphology change, which leads to the differentiated accumulation of boron inside cells. Overall, the optimized boron-bearing assembly precursor could significantly improve the boron accumulation compared with BPA in cancer cells. In this study, we have demonstrated a convenient method to introduce boron agents to cancer cells. We envision that the EISA-mediated accumulation of boron will be helpful in the design of boron agents to facilitate BNCT treatment.

Controlling the Chain Folding for the Synthesis of Single-Chain Polymer Nanoparticles Using Thermoresponsive Polymers

Synthetic polymer single-chain nanoparticles (SCNPs) are an emerging new class of nanomaterials that possess similar folded structures as natural proteins. However, most SCNPs reported so far are p...

Effects of ionic liquid doping on gas transport properties of thermally rearranged poly(hydroxyimide)s

In this study we present a novel and simple approach to improve the gas separation performance of the thermally rearranged membranes, which involves doping the polyimide precursors (HPI) with ionic liquid (IL), and carrying out its degradation along with the conversion process to polybenzoxazole (PBO) in order to facilitate the formation of larger and /or more numerous free volumes. A series of aromatic (co)poly(hydroxyimide)s based on 6FDA and HAB/4MPD diamines in different molar ratios, as well as BPADA-HAB poly(hydroxyimide) were synthesized as the precursors to be doped with IL and thermally rearranged to PBO. The structural modifications of the precursor backbone were applied to study the impact of IL on the physical properties, thermal conversion process, as well as gas transport properties of the doped polymers with different chain rigidities. The pure and IL doped (co)polyimides and their thermally rearranged counterparts were characterized by WAXD, DSC, TGA, tensile tests, and PALS, and examined in pure gas permeation experiments. TR conversion temperature was considerably reduced by IL doping (e.g. by 126 °C). This effect depended on the precursor chemical structure and the IL content. After thermal rearrangement of the IL doped HPIs, the membrane permeability to gases increased significantly compared to the un-doped analogues (e.g. 2 fold increase for O2 permeability). The permeability increase was larger for the higher IL content and the precursor chain rigidity. This was accompanied by a relatively small loss in selectivity leading to the performance shift towards the 2008 upper bound. The differences in permeability among the samples correlated with the free volume size from PALS. In particular, a very good correlation was obtained (r2 = 0.958), when the data fitted to the Cohen-Turnbull model concerned only PBO samples with low cohesive energy density. Further studies on HPIs doped with IL with lower degradation temperatures are suggested to mitigate polymer degradation and explore this new method for the design of improved gas separation membrane materials.

A facile synthesis of hierarchical flower-like TiO2 wrapped with MoS2 sheets nanostructure for enhanced electrorheological activity

Flower-like TiO2@MoS2 nanocomposite with a hierarchical and core@shell structure was synthesized using a two-step hydrothermal method, in which the flower-like Ti-containing precursor backbone was initially prepared to provide a large surface to enable the MoS2 sheets to coat on TiO2 uniformly. The glucose and acetate ion (Ac−1) were found to play a crucial role in the formation of the intimate interface between TiO2 and MoS2. The hierarchical composite was dispersed in silicone oil as ER fluids at 10 wt%, which exhibited a high ER efficiency by combining the advantages of TiO2 hierarchical structures and suitable conductivity of MoS2 sheets. The high polarization strength and suitable dielectric relaxation of ER fluid was obtained under electric fields, which leaded to the improvement of interfacial polarization and ER activity.

Click-based transparent durable films derived from tetrabrachius PDMS-bridged epoxy acrylates and surface modified nanosilica particles

Abstract We propose a novel tetra-arm polydimethylsiloxane-bridged aryl-ether-functional epoxy acrylate (EAAE-PDMS), which was employed as a precursor to crosslink with systematic variations (0, 1, 3, 5, 15 wt.%) of thiol-functionalized silica nanoparticles (SNs) through a thiol-ene click chemistry, resulting in transparent hybrid films (EAAE-PDMS@SiO 2 ). The unique tetrabrachius structure of EAAE-PDMS can result in significantly high crosslinking densities and high gel content of their thermosetts. The introduction of PDMS bridge in the precursor backbone and the modification of SNs are simultaneously in favor of better compatibility between the organic/inorganic components, benefiting for the distinctly improved surface mechanical properties namely scratch hardness and abrasion resistance relative to common epoxy acrylates. A sound proof is the fact that either our hybrid film derived from neat EAAE-PDMS or its mixture with thiol-functionalized SNs shows an increased 5%-mass-loss temperature at least by 90 °C and up to 7-fold enhancement in the abrasion resistance relative to the silica-free EA film. Finally, the as-made films show excellent solvent and thermal resistance and strong adhesion, providing strong potentials for application in dielectric and mechanic materials.

Artificial miRNA-mediated silencing of ecdysone receptor (EcR) affects larval development and oogenesis in Helicoverpa armigera

The insect pests are real threat to farmers as they affect the crop yield to a great extent. The use of chemical pesticides for insect pest control has always been a matter of concern as they pollute the environment and are also harmful for human health. Bt (Bacillus thuringensis) technology helped the farmers to get rid of the insect pests, but experienced a major drawback due to the evolution of insects gaining resistance towards these toxins. Hence, alternative strategies are high on demand to control insect pests. RNA-based gene silencing is emerging as a potential tool to tackle with this problem. In this study, we have shown the use of artificial microRNA (amiRNA) to specifically target the ecdysone receptor (EcR) gene of Helicoverpa armigera (cotton bollworm), which attacks several important crops like cotton, tomato chickpea, pigeon pea, etc and causes huge yield losses. Insect let-7a precursor miRNA (pre-miRNA) backbone was used to replace the native miRNA with that of amiRNA. The precursor backbone carrying the 21 nucleotide amiRNA sequence targeting HaEcR was cloned in bacterial L4440 vector for in vitro insect feeding experiments. Larvae fed with Escherichia coli expressing amiRNA-HaEcR showed a reduction in the expression of target gene as well as genes involved in the ecdysone signaling pathway downstream to EcR and exhibited mortality and developmental defects. Stem-loop RT-PCR revealed the presence of amiRNA in the insect larvae after feeding bacteria expressing amiRNA-HaEcR, which was otherwise absent in controls. We also found a significant drop in the reproduction potential (oogenesis) of moths which emerged from treated larvae as compared to control. These results demonstrate the successful use of an insect pre-miRNA backbone to express amiRNA for gene silencing studies in insects. The method is cost effective and can be exploited as an efficient and alternative tool for insect pest management.

Evaluation and identification of candidate genes for artificial microRNA-mediated resistance to tomato spotted wilt virus

Tomato spotted wilt virus (TSWV) is an economically important viral pathogen of a wide range of field and horticultural crops. We developed an artificial microRNA (amiRNA) strategy against TSWV, targeting the nucleoprotein (N) and silencing suppressor (NSs) genes. The amiRNA constructs replaced the natural miRNA in a shortened Arabidopsis 173-nucleotide (nt) miR159a precursor backbone (athmiR159a) without the stem base extending beyond the miR/miR* duplex. Further, each amiRNA was modified to contain a mismatch (wobble) sequence at nucleotide position 12 and 13 on the complementary strand amiRNA*, mimicking the endogenous miR159a sequence structure. Transient expression in Nicotiana benthamiana demonstrated that the introduction of a wobble sequence did not alter amiRNA expression levels. Following challenge inoculation with TSWV, plants expressing N-specific amiRNAs with or without the wobble remained asymptomatic and were negative for TSWV by ELISA. In contrast, plants expressing the NSs-specific amiRNAs were symptomatic and accumulated high levels of TSWV. Similar findings were obtained in stably transformed Nicotiana tabacum plants. Our results show that a shortened 173-nt athmiR159a backbone is sufficient to express amiRNAs and that the presence of mismatch at position 12–13 does not influence amiRNA expression or conferring of resistance. We also show that selection of target gene and positional effect are critical in amiRNA-based approach for introducing resistance. These findings open the possibility of employing the amiRNA approach for broad-spectrum resistance to tospoviruses as well as other viruses.

Temperature dependence of gas transport and sorption in carbon molecular sieve membranes derived from four 6FDA based polyimides: Entropic selectivity evaluation

Temperature dependences of gas transport and sorption properties on four previously isothermally studied 6FDA based carbon molecular sieve (CMS) membranes: 6FDA/DETDA, 6FDA:BPDA(1:1)/DETDA, 6FDA/DETDA:DABA(3:2) and 6FDA/1,5-ND:ODA(1:1), were examined over the temperature range from 35 °C to 50 °C. The permeability, sorption and diffusivity of these materials are reported, and activation energies of permeation and diffusion as well as heats of sorption for gases CO2, CH4, O2, and N2 of these materials are compared. Permselectivity of these materials at 35 °C was probed for three gas pairs: CO2/CH4, O2/N2, and N2/CH4, and results show that diffusion selectivity is the dominant factor in providing permselectivity. Diffusion selectivity can be factored further into an energetic selectivity and an entropic selectivity. The temperature dependence of both energetic and entropic selectivity and their contributions to overall diffusion selectivity are discussed in detail in this study. All four CMS membranes showed larger than unity entropic selectivity discriminations. 6FDA/DETDA derived CMS membrane, with the most compact structure, showed the largest entropic selectivity for CO2/CH4, O2/N2, and N2/CH4 as about 7.40, 4.24, and 2.17 respectively. Analysis of the selectivity factors provides insights into the effects of polymer precursor backbone structures on key transport and sorption properties in CMS materials.

Polycistronic artificial miRNA-mediated resistance to Wheat dwarf virus in barley is highly efficient at low temperature.

Infection of Wheat dwarf virus (WDV) strains on barley results in dwarf disease, imposing severe economic losses on crop production. As the natural resistance resources against this virus are limited, it is imperative to elaborate a biotechnological approach that will provide effective and safe immunity to a wide range of WDV strains. Because vector insect-mediated WDV infection occurs during cool periods in nature, it is important to identify a technology which is effective at lower temperature. In this study, we designed artificial microRNAs (amiRNAs) using a barley miRNA precursor backbone, which target different conservative sequence elements of the WDV strains. Potential amiRNA sequences were selected to minimize the off-target effects and were tested in a transient sensor system in order to select the most effective constructs at low temperature. On the basis of the data obtained, a polycistronic amiRNA precursor construct (VirusBuster171) was built expressing three amiRNAs simultaneously. The construct was transformed into barley under the control of a constitutive promoter. The transgenic lines were kept at 12-15 °C to mimic autumn and spring conditions in which major WDV infection and accumulation take place. We were able to establish a stable barley transgenic line displaying resistance to insect-mediated WDV infection. Our study demonstrates that amiRNA technology can be an efficient tool for the introduction of highly efficient resistance in barley against a DNA virus belonging to the Geminiviridae family, and this resistance is effective at low temperature where the natural insect vector mediates the infection process.

Transgene-induced gene silencing in plants.

RNAi is the most important reverse genetics tool to trigger transgenic gene silencing, which is now applied widely to investigate gene function and also practically applied to enhance resistance to biotic and abiotic stress. Recently, the most effective way to induce transgenic gene silencing is to introduce inverted repeat (IR) double-stranded RNA (dsRNA) or artificial microRNA (amiRNA) instead of a transgenic sense or antisense strand of genes. The stable transgenic plants can be acquired through Agrobacterium tumefaciens-mediated transformation of binary vectors containing an RNAi hairpin construct or amiRNA precursor backbone sequence. Here we primarily describe these two methods' vector construction, plant transformation, and transgenic line verification.

Manoyl Oxide (13R), the Biosynthetic Precursor of Forskolin, Is Synthesized in Specialized Root Cork Cells in Coleus forskohlii

Forskolin, a complex labdane diterpenoid found in the root of Coleus forskohlii (Lamiaceae), has received attention for its broad range of pharmacological activities, yet the biosynthesis has not been elucidated. We detected forskolin in the root cork of C. forskohlii in a specialized cell type containing characteristic structures with histochemical properties consistent with oil bodies. Organelle purification and chemical analysis confirmed the localization of forskolin and of its simplest diterpene precursor backbone, (13R) manoyl oxide, to the oil bodies. The labdane diterpene backbone is typically synthesized by two successive reactions catalyzed by two distinct classes of diterpene synthases. We have recently described the identification of a small gene family of diterpene synthase candidates (CfTPSs) in C. forskohlii. Here, we report the functional characterization of four CfTPSs using in vitro and in planta assays. CfTPS2, which synthesizes the intermediate copal-8-ol diphosphate, in combination with CfTPS3 resulted in the stereospecific formation of (13R) manoyl oxide, while the combination of CfTPS1 and CfTPS3 or CfTPS4 led to formation of miltiradiene, precursor of abietane diterpenoids in C. forskohlii. Expression profiling and phylogenetic analysis of the CfTPS family further support the functional diversification and distinct roles of the individual diterpene synthases and the involvement of CfTPS1 to CfTPS4 in specialized metabolism and of CfTPS14 and CfTPS15 in general metabolism. Our findings pave the way toward the discovery of the remaining components of the pathway to forskolin, likely localized in this specialized cell type, and support a role of oil bodies as storage organelles for lipophilic bioactive metabolites.

A Novel Fatty Acyl Desaturase from the Pheromone Glands of Ctenopseustis obliquana and C. herana with Specific Z5-Desaturase Activity on Myristic Acid

Sexual communication in the Lepidoptera typically involves a female-produced sex pheromone that attracts males of the same species. The most common type of moth sex pheromone comprises individual or blends of fatty acyl derivatives that are synthesized by a specific enzymatic pathway in the female’s pheromone gland, often including a desaturation step. This reaction is catalyzed by fatty acyl desaturases that introduce double bonds at specific locations in the fatty acid precursor backbone. The two tortricid moths, Ctenopseustis obliquana and C. herana (brown-headed leafrollers), which are endemic in New Zealand, both use (Z)-5-tetradecenyl acetate as part of their sex pheromone. In C. herana, (Z)-5-tetradecenyl acetate is the sole component of the pheromone. Labeling experiments have revealed that this compound is produced via an unusual Δ5-desaturation of myristic acid. Previously six desaturases were identified from the pheromone glands of Ctenopseustis and its sibling genus Planotortrix, with one differentially regulated to produce the distinct blends used by individual species. However, none were able to conduct the Δ5-desaturation observed in C. herana, and presumably C. obliquana. We have now identified an additional desaturase gene, desat7, expressed in the pheromone glands of both Ctenopseustis species, which is not closely related to any previously described moth pheromone desaturase. The encoded enzyme displays Δ5-desaturase activity on myristic acid when heterologously expressed in yeast, but is not able to desaturate any other fatty acid (C8–C16). We conclude that desat7 represents a new group of desaturases that has evolved a role in the biosynthesis of sex pheromones in moths.Electronic supplementary materialThe online version of this article (doi:10.1007/s10886-013-0373-1) contains supplementary material, which is available to authorized users.

Green and Blue Electrochromic Polymers from Processable Siloxane Precursors

Herein we report the synthesis of a new class of processable siloxane precursor polymers consisting of aromatic groups and flexible siloxane linkages and their conversions to green and blue electrochromic polymers in the solid state. 3,4-Ethylenedioxythiophene (EDOT), 2,2′-bis(3,4-ethylenedioxythiophene) (BiEDOT), and a donor–acceptor moiety 4,7-bis(EDOT)-2,1,3-benzothiadiazole (BEBTD) were incorporated as aromatic groups to demonstrate the versatility of the precursor method to different aromatic systems. The utilization of a siloxane linkage allows for a precursor polymer exhibiting improved solubility in common organic solvents and accessible glass transition temperatures (−1 to 132 °C) as compared to a previously reported silane precursor. A simple method to control the thermal properties of the precursor was also demonstrated by incorporation of both siloxane and silane functionalities into the precursor backbone. The oxidatively converted product from the precursors showed electronic and optoelectronic properties comparable to the conjugated polymer prepared by conventional electrochemical polymerization of monomers in an electrolyte bath. In addition to the dark-blue to sky-blue electrochromic PEDOT from EDOT and BiEDOT, a dual-band absorbing green to sky-blue electrochromic polymer was demonstrated using BEBTD. This demonstrates that the precursor approach is easily applicable and feasible for the preparation of conjugated polymers from numerable electrochemically polymerizable aromatic groups.

A convenient method for the synthesis of phosphoramidite non-nucleotide inserts for preparation of functionalized oligonucleotides

A simple approach to the synthesis of amidophosphite synthons of achiral non-nucleotide inserts using 4-(2-(4,4′-dimethoxytrityloxy)ethyl)morpholine-2,3-dione as a backbone of key precursor was suggested. Non-nucleotide synthons were synthesized using this approach that were suitable for synthesis of acridine-containing oligonucleotide derivatives, as well as oligonucleotides with branched carbohydrate-phosphate backbone.

Characterization of uniformly and atom-specifically 13C-labeled heparin and heparan sulfate polysaccharide precursors using 13C NMR spectroscopy and ESI mass spectrometry

The biological actions of heparin and heparan sulfate, two structurally related glycosaminoglycans, depend on the organization of the complex heparanome. Due to the structural complexity of the heparanome, the sequence of variably sulfonated uronic acid and glucosamine residues is usually characterized by the analysis of smaller oligosaccharide and disaccharide fragments. Even characterization of smaller heparin and heparan sulfate oligosaccharide or disaccharide fragments using simple 1D 1H NMR spectroscopy is often complicated by the extensive signal overlap. 13C NMR signals, on the other hand, overlap less and therefore, 13C NMR spectroscopy can greatly facilitate the structural elucidation of the complex heparanome and provide finer insights into the structural basis for biological functions. This is the first report of the preparation of anomeric carbon-specific 13C-labeled heparin and heparan sulfate precursors from the Escherichia coli K5 strain. Uniformly 13C- and 15N-labeled precursors were also produced and characterized by 13C NMR spectroscopy. Mass spectrometric analysis of enzymatically fragmented disaccharides revealed that anomeric carbon-specific labeling efforts resulted in a minor loss/scrambling of 13C in the precursor backbone, whereas uniform labeling efforts resulted in greater than 95% 13C isotope enrichment in the precursor backbone. These labeled precursors provided high-resolution NMR signals with great sensitivity and set the stage for studying the heparanome–proteome interactions.

Arylene Imine Macrocycles of C3h and C3 Symmetry from Reductive Imination of Nitroformylarenes

Novel C(3)-symmetric phenylene imine macrocycles have been synthesized by reductive imination of single nitroformylarenes. Pore size and geometric shape are dictated by the distance between and orientation of the nitro and aldehyde moieties in the precursor backbone. This reaction is facile, requires no purification of the products, and is environmentally friendly.

The Drosophila Inhibitor of Apoptosis (IAP) DIAP2 Is Dispensable for Cell Survival, Required for the Innate Immune Response to Gram-negative Bacterial Infection, and Can Be Negatively Regulated by the Reaper/Hid/Grim Family of IAP-binding Apoptosis Inducers

Many inhibitor of apoptosis (IAP) family proteins inhibit apoptosis. IAPs contain N-terminal baculovirus IAP repeat domains and a C-terminal RING ubiquitin ligase domain. Drosophila IAP DIAP1 is essential for the survival of many cells, protecting them from apoptosis by inhibiting active caspases. Apoptosis initiates when proteins such as Reaper, Hid, and Grim bind a surface groove in DIAP1 baculovirus IAP repeat domains via an N-terminal IAP-binding motif. This evolutionarily conserved interaction disrupts DIAP1-caspase interactions, unleashing apoptosis-inducing caspase activity. A second Drosophila IAP, DIAP2, also binds Rpr and Hid and inhibits apoptosis in multiple contexts when overexpressed. However, due to a lack of mutants, little is known about the normal functions of DIAP2. We report the generation of diap2 null mutants. These flies are viable and show no defects in developmental or stress-induced apoptosis. Instead, DIAP2 is required for the innate immune response to Gram-negative bacterial infection. DIAP2 promotes cytoplasmic cleavage and nuclear translocation of the NF-kappaB homolog Relish, and this requires the DIAP2 RING domain. Increasing the genetic dose of diap2 results in an increased immune response, whereas expression of Rpr or Hid results in down-regulation of DIAP2 protein levels. Together these observations suggest that DIAP2 can regulate immune signaling in a dose-dependent manner, and this can be regulated by IBM-containing proteins. Therefore, diap2 may identify a point of convergence between apoptosis and immune signaling pathways.