Mammal responses to global changes in human activity vary by trophic group and landscape.

Wildlife must adapt to human presence to survive in the Anthropocene, so it is critical to understand species responses to humans in different contexts. We used camera trapping as a lens to view mammal responses to changes in human activity during the COVID-19 pandemic. Across 163 species sampled in 102 projects around the world, changes in the amount and timing of animal activity varied widely. Under higher human activity, mammals were less active in undeveloped areas but unexpectedly more active in developed areas while exhibiting greater nocturnality. Carnivores were most sensitive, showing the strongest decreases in activity and greatest increases in nocturnality. Wildlife managers must consider how habituation and uneven sensitivity across species may cause fundamental differences in human-wildlife interactions along gradients of human influence.

Distance from human settlements favors wild-type appearance of feral cats (Felis catus) in Mediterranean woodland.

Camouflage is a common trait enabling animals to avoid detection by predators and prey. Patterns such as spots and stripes are convergent across carnivore families, including felids, and are hypothesized to have adaptive value through camouflage. House cats (Felis catus) were domesticated thousands of years ago, but despite artificial selection for a wide variety of coat colors, the wild-type pattern of tabby cats is very common. We aimed to determine whether this pattern grants an advantage over other morphs in natural environments. We collected cat images taken with camera traps in natural areas near and far from 38 rural settlements in Israel, to compare the habitat use by feral cats of different colors. We tested the effect of proximity to villages and habitat vegetation (normalized difference vegetation index, NDVI) on the probability of space use by the tabby morph compared to the others. NDVI had a positive effect on site use in both morphs, but non-tabby cats had a 2.1 higher probability of using the near sites than the far sites, independent of NDVI. The wild-type tabby cats' probability of site use were equally likely to be unaffected by proximity, or have an interaction of proximity with NDVI whereby the far transects are used with increasing probability in sites of denser vegetation. We hypothesize that the camouflage of tabby cats, more than other colors and patterns, confers an advantage in roaming the woodland habitats for which this pattern evolved. This has both theoretical implications as rare empirical evidence of the adaptive value of fur coloration, and practical implications on managing the ecological impact of feral cats worldwide.

Physical and functional interaction between SET1/COMPASS complex component CFP-1 and a Sin3S HDAC complex in C. elegans.

The CFP1 CXXC zinc finger protein targets the SET1/COMPASS complex to non-methylated CpG rich promoters to implement tri-methylation of histone H3 Lys4 (H3K4me3). Although H3K4me3 is widely associated with gene expression, the effects of CFP1 loss vary, suggesting additional chromatin factors contribute to context dependent effects. Using a proteomics approach, we identified CFP1 associated proteins and an unexpected direct link between Caenorhabditis elegans CFP-1 and an Rpd3/Sin3 small (SIN3S) histone deacetylase complex. Supporting a functional connection, we find that mutants of COMPASS and SIN3 complex components genetically interact and have similar phenotypic defects including misregulation of common genes. CFP-1 directly binds SIN-3 through a region including the conserved PAH1 domain and recruits SIN-3 and the HDA-1/HDAC subunit to H3K4me3 enriched promoters. Our results reveal a novel role for CFP-1 in mediating interaction between SET1/COMPASS and a Sin3S HDAC complex at promoters.

Chromatin accessibility dynamics across C. elegans development and ageing.

An essential step for understanding the transcriptional circuits that control development and physiology is the global identification and characterization of regulatory elements. Here, we present the first map of regulatory elements across the development and ageing of an animal, identifying 42,245 elements accessible in at least one Caenorhabditis elegans stage. Based on nuclear transcription profiles, we define 15,714 protein-coding promoters and 19,231 putative enhancers, and find that both types of element can drive orientation-independent transcription. Additionally, more than 1000 promoters produce transcripts antisense to protein coding genes, suggesting involvement in a widespread regulatory mechanism. We find that the accessibility of most elements changes during development and/or ageing and that patterns of accessibility change are linked to specific developmental or physiological processes. The map and characterization of regulatory elements across C. elegans life provides a platform for understanding how transcription controls development and ageing.

Long noncoding RNA EWSAT1-mediated gene repression facilitates Ewing sarcoma oncogenesis.

Chromosomal translocation that results in fusion of the genes encoding RNA-binding protein EWS and transcription factor FLI1 (EWS-FLI1) is pathognomonic for Ewing sarcoma. EWS-FLI1 alters gene expression through mechanisms that are not completely understood. We performed RNA sequencing (RNAseq) analysis on primary pediatric human mesenchymal progenitor cells (pMPCs) expressing EWS-FLI1 in order to identify gene targets of this oncoprotein. We determined that long noncoding RNA-277 (Ewing sarcoma-associated transcript 1 [EWSAT1]) is upregulated by EWS-FLI1 in pMPCs. Inhibition of EWSAT1 expression diminished the ability of Ewing sarcoma cell lines to proliferate and form colonies in soft agar, whereas EWSAT1 inhibition had no effect on other cell types tested. Expression of EWS-FLI1 and EWSAT1 repressed gene expression, and a substantial fraction of targets that were repressed by EWS-FLI1 were also repressed by EWSAT1. Analysis of RNAseq data from primary human Ewing sarcoma further supported a role for EWSAT1 in mediating gene repression. We identified heterogeneous nuclear ribonucleoprotein (HNRNPK) as an RNA-binding protein that interacts with EWSAT1 and found a marked overlap in HNRNPK-repressed genes and those repressed by EWS-FLI1 and EWSAT1, suggesting that HNRNPK participates in EWSAT1-mediated gene repression. Together, our data reveal that EWSAT1 is a downstream target of EWS-FLI1 that facilitates the development of Ewing sarcoma via the repression of target genes.

Comparative analysis of metazoan chromatin organization.

Genome function is dynamically regulated in part by chromatin, which consists of the histones, non-histone proteins and RNA molecules that package DNA. Studies in Caenorhabditis elegans and Drosophila melanogaster have contributed substantially to our understanding of molecular mechanisms of genome function in humans, and have revealed conservation of chromatin components and mechanisms. Nevertheless, the three organisms have markedly different genome sizes, chromosome architecture and gene organization. On human and fly chromosomes, for example, pericentric heterochromatin flanks single centromeres, whereas worm chromosomes have dispersed heterochromatin-like regions enriched in the distal chromosomal 'arms', and centromeres distributed along their lengths. To systematically investigate chromatin organization and associated gene regulation across species, we generated and analysed a large collection of genome-wide chromatin data sets from cell lines and developmental stages in worm, fly and human. Here we present over 800 new data sets from our ENCODE and modENCODE consortia, bringing the total to over 1,400. Comparison of combinatorial patterns of histone modifications, nuclear lamina-associated domains, organization of large-scale topological domains, chromatin environment at promoters and enhancers, nucleosome positioning, and DNA replication patterns reveals many conserved features of chromatin organization among the three organisms. We also find notable differences in the composition and locations of repressive chromatin. These data sets and analyses provide a rich resource for comparative and species-specific investigations of chromatin composition, organization and function.

PRDE-1 is a nuclear factor essential for the biogenesis of Ruby motif-dependent piRNAs in C. elegans.

Piwi-interacting RNAs (piRNA) are small regulatory RNAs with essential roles in maintaining genome integrity in animals and protists. Most Caenorhabditis elegans piRNAs are transcribed from two genomic clusters that likely contain thousands of individual transcription units; however, their biogenesis is not understood. Here we identify and characterize prde-1 (piRNA silencing-defective) as the first essential C. elegans piRNA biogenesis gene. Analysis of prde-1 provides the first direct evidence that piRNA precursors are 28- to 29-nucleotide (nt) RNAs initiating 2 nt upstream of mature piRNAs. PRDE-1 is a nuclear germline-expressed protein that localizes to chromosome IV. PRDE-1 is required specifically for the production of piRNA precursors from genomic loci containing an 8-nt upstream motif, the Ruby motif. The expression of a second class of motif-independent piRNAs is unaffected in prde-1 mutants. We exploited this finding to determine the targets of the motif-independent class of piRNAs. Together, our data provide new insights into both the biogenesis and function of piRNAs in gene regulation.

Extreme HOT regions are CpG-dense promoters in C. elegans and humans.

Most vertebrate promoters lie in unmethylated CpG-dense islands, whereas methylation of the more sparsely distributed CpGs in the remainder of the genome is thought to contribute to transcriptional repression. Nonmethylated CG dinucleotides are recognized by CXXC finger protein 1 (CXXC1, also known as CFP1), which recruits SETD1A (also known as Set1) methyltransferase for trimethylation of histone H3 lysine 4, an active promoter mark. Genomic regions enriched for CpGs are thought to be either absent or irrelevant in invertebrates that lack DNA methylation, such as C. elegans; however, a CXXC1 ortholog (CFP-1) is present. Here we demonstrate that C. elegans CFP-1 targets promoters with high CpG density, and these promoters are marked by high levels of H3K4me3. Furthermore, as for mammalian promoters, high CpG content is associated with nucleosome depletion irrespective of transcriptional activity. We further show that highly occupied target (HOT) regions identified by the binding of a large number of transcription factors are CpG-rich promoters in C. elegans and human genomes, suggesting that the unusually high factor association at HOT regions may be a consequence of CpG-linked chromatin accessibility. Our results indicate that nonmethylated CpG-dense sequence is a conserved genomic signal that promotes an open chromatin state, targeting by a CXXC1 ortholog, and H3K4me3 modification in both C. elegans and human genomes.

A meta-analysis of lung cancer gene expression identifies PTK7 as a survival gene in lung adenocarcinoma.

Lung cancer remains the most common cause of cancer-related death worldwide and it continues to lack effective treatment. The increasingly large and diverse public databases of lung cancer gene expression constitute a rich source of candidate oncogenic drivers and therapeutic targets. To define novel targets for lung adenocarcinoma, we conducted a large-scale meta-analysis of genes specifically overexpressed in adenocarcinoma. We identified an 11-gene signature that was overexpressed consistently in adenocarcinoma specimens relative to normal lung tissue. Six genes in this signature were specifically overexpressed in adenocarcinoma relative to other subtypes of non-small cell lung cancer (NSCLC). Among these genes was the little studied protein tyrosine kinase PTK7. Immunohistochemical analysis confirmed that PTK7 is highly expressed in primary adenocarcinoma patient samples. RNA interference-mediated attenuation of PTK7 decreased cell viability and increased apoptosis in a subset of adenocarcinoma cell lines. Further, loss of PTK7 activated the MKK7-JNK stress response pathway and impaired tumor growth in xenotransplantation assays. Our work defines PTK7 as a highly and specifically expressed gene in adenocarcinoma and a potential therapeutic target in this subset of NSCLC.

Two is better than one: combining IGF1R and MEK blockade as a promising novel treatment strategy against KRAS-mutant lung cancer.

A small-molecule inhibitor screen on a panel of human lung cancer cell lines has uncovered an unexpected sensitivity of cells expressing oncogenic KRAS toward insulin-like growth factor 1 receptor (IGF1R) inhibition. Combining IGF1R and MAP-ERK kinase blockade led to significant effects on viability in human non-small cell lung cancer (NSCLC) cell lines and in 2 mouse models of oncogenic KRAS-driven lung cancer. The mechanistic basis for this effect seems to be an increased baseline activation of IGF1R-mediated activation of AKT in cells that express oncogenic KRAS. The studies thus point to a novel approach for treatment of KRAS-driven NSCLC, a particularly difficult subset of patients to treat with existing approaches.

The landscape of RNA polymerase II transcription initiation in C. elegans reveals promoter and enhancer architectures.

RNA polymerase transcription initiation sites are largely unknown in Caenorhabditis elegans. The initial 5' end of most protein-coding transcripts is removed by trans-splicing, and noncoding initiation sites have not been investigated. We characterized the landscape of RNA Pol II transcription initiation, identifying 73,500 distinct clusters of initiation. Bidirectional transcription is frequent, with a peak of transcriptional pairing at 120 bp. We assign transcription initiation sites to 7691 protein-coding genes and find that they display features typical of eukaryotic promoters. Strikingly, the majority of initiation events occur in regions with enhancer-like chromatin signatures. Based on the overlap of transcription initiation clusters with mapped transcription factor binding sites, we define 2361 transcribed intergenic enhancers. Remarkably, productive transcription elongation across these enhancers is predominantly in the same orientation as that of the nearest downstream gene. Directed elongation from an upstream enhancer toward a downstream gene could potentially deliver RNA polymerase II to a proximal promoter, or alternatively might function directly as a distal promoter. Our results provide a new resource to investigate transcription regulation in metazoans.

Cross-species functional analysis of cancer-associated fibroblasts identifies a critical role for CLCF1 and IL-6 in non-small cell lung cancer in vivo.

Cancer-associated fibroblasts (CAF) have been reported to support tumor progression by a variety of mechanisms. However, their role in the progression of non-small cell lung cancer (NSCLC) remains poorly defined. In addition, the extent to which specific proteins secreted by CAFs contribute directly to tumor growth is unclear. To study the role of CAFs in NSCLCs, a cross-species functional characterization of mouse and human lung CAFs was conducted. CAFs supported the growth of lung cancer cells in vivo by secretion of soluble factors that directly stimulate the growth of tumor cells. Gene expression analysis comparing normal mouse lung fibroblasts and mouse lung CAFs identified multiple genes that correlate with the CAF phenotype. A gene signature of secreted genes upregulated in CAFs was an independent marker of poor survival in patients with NSCLC. This secreted gene signature was upregulated in normal lung fibroblasts after long-term exposure to tumor cells, showing that lung fibroblasts are "educated" by tumor cells to acquire a CAF-like phenotype. Functional studies identified important roles for CLCF1-CNTFR and interleukin (IL)-6-IL-6R signaling in promoting growth of NSCLCs. This study identifies novel soluble factors contributing to the CAF protumorigenic phenotype in NSCLCs and suggests new avenues for the development of therapeutic strategies.

miRNA-125b regulates TNF-α production in CD14+ neonatal monocytes via post-transcriptional regulation.

Neonates, although deficient in cell immunity, frequently reveal sepsis with augmented proinflammatory reactions. Here, we found that neonatal monocytes produced significantly higher TNF-α mRNA and protein than adult monocytes. Assessment of the transcriptional factor found no significant difference of NF-κB p65 level between neonatal and adult monocytes. Addition of Act D to access the half-life of TNF-α mRNA revealed no significant difference of the LPS-induced TNF-α mRNA half-life between them, whereas CHX increased neonatal TNF-α mRNA significantly. This suggests that a post-transcriptional mechanism involves the augmentation of TNF-α production by neonatal monocytes. To examine whether miRNA was involved in the post-transcriptional regulation, differential displays of miRNA array between neonatal and adult MNCs were performed, along with the discovery of hsa-miR-103, hsa-miR-125b, hsa-miR-130a, hsa-miR-454-3p, and hsa-miR-542-3p, which were greater than a twofold decrease or increase after LPS treatment for 4 h. The functional validation identified that miR-125b decreased significantly in association with higher TNF-α expression by neonatal monocytes after LPS stimulation. Transfection of the miR-125b precursor into neonatal monocytes significantly repressed the TNF-α mRNA and protein expression, suggesting that miR-125b negatively regulates TNF-α expression in neonatal monocytes. Modulation of miRNA expression may be used to regulate TNF-α production in newborns with altered proinflammatory reactions.

How vaccinia virus has evolved to subvert the host immune response.

Viruses are obligate intracellular parasites and are some of the most rapidly evolving and diverse pathogens encountered by the host immune system. Large complicated viruses, such as poxviruses, have evolved a plethora of proteins to disrupt host immune signalling in their battle against immune surveillance. Recent X-ray crystallographic analysis of these viral immunomodulators has helped form an emerging picture of the molecular details of virus-host interactions. In this review we consider some of these immune evasion strategies as they apply to poxviruses, from a structural perspective, with specific examples from the European SPINE2-Complexes initiative. Structures of poxvirus immunomodulators reveal the capacity of viruses to mimic and compete against the host immune system, using a diverse range of structural folds that are unique or acquired from their hosts with both enhanced and unexpectedly divergent functions.

Wilms tumor 1 (WT1) regulates KRAS-driven oncogenesis and senescence in mouse and human models.

KRAS is one of the most frequently mutated human oncogenes. In some settings, oncogenic KRAS can trigger cellular senescence, whereas in others it produces hyperproliferation. Elucidating the mechanisms regulating these 2 drastically distinct outcomes would help identify novel therapeutic approaches in RAS-driven cancers. Using a combination of functional genomics and mouse genetics, we identified a role for the transcription factor Wilms tumor 1 (WT1) as a critical regulator of senescence and proliferation downstream of oncogenic KRAS signaling. Deletion or suppression of Wt1 led to senescence of mouse primary cells expressing physiological levels of oncogenic Kras but had no effect on wild-type cells, and Wt1 loss decreased tumor burden in a mouse model of Kras-driven lung cancer. In human lung cancer cell lines dependent on oncogenic KRAS, WT1 loss decreased proliferation and induced senescence. Furthermore, WT1 inactivation defined a gene expression signature that was prognostic of survival only in lung cancer patients exhibiting evidence of oncogenic KRAS activation. These findings reveal an unexpected role for WT1 as a key regulator of the genetic network of oncogenic KRAS and provide important insight into the mechanisms that regulate proliferation or senescence in response to oncogenic signals.

Multimodality imaging of gene transfer with a receptor-based reporter gene.

UNLABELLED: Gene therapy trials have traditionally used tumor and tissue biopsies for assessing the efficacy of gene transfer. Noninvasive imaging techniques offer a distinct advantage over tissue biopsies in that the magnitude and duration of gene transfer can be monitored repeatedly. Human somatostatin receptor subtype 2 (SSTR2) has been used for the nuclear imaging of gene transfer. To extend this concept, we have developed a somatostatin receptor-enhanced green fluorescent protein fusion construct (SSTR2-EGFP) for nuclear and fluorescent multimodality imaging. METHODS: An adenovirus containing SSTR2-EGFP (AdSSTR2-EGFP) was constructed and evaluated in vitro and in vivo. SCC-9 human squamous cell carcinoma cells were infected with AdEGFP, AdSSTR2, or AdSSTR2-EGFP for in vitro evaluation by saturation binding, internalization, and fluorescence spectroscopy assays. In vivo biodistribution and nano-SPECT imaging studies were conducted with mice bearing SCC-9 tumor xenografts directly injected with AdSSTR2-EGFP or AdSSTR2 to determine the tumor localization of (111)In-diethylenetriaminepentaacetic acid (DTPA)-Tyr3-octreotate. Fluorescence imaging was conducted in vivo with mice receiving intratumoral injections of AdSSTR2, AdSSTR2-EGFP, or AdEGFP as well as ex vivo with tissues extracted from mice. RESULTS: The similarity between AdSSTR2-EGFP and wild-type AdSSTR2 was demonstrated in vitro by the saturation binding and internalization assays, and the fluorescence emission spectra of cells infected with AdSSTR2-EGFP was almost identical to the spectra of cells infected with wild-type AdEGFP. Biodistribution studies demonstrated that the tumor uptake of (111)In-DTPA-Tyr3-octreotate was not significantly different (P > 0.05) when tumors (n = 5) were injected with AdSSTR2 or AdSSTR2-EGFP but was significantly greater than the uptake in control tumors. Fluorescence was observed in tumors injected with AdSSTR2-EGFP and AdEGFP in vivo and ex vivo but not in tumors injected with AdSSTR2. Although fluorescence was observed, there were discrepancies between in vivo imaging and ex vivo imaging as well as between nuclear imaging and fluorescent imaging. CONCLUSION: These studies showed that the SSTR2-EGFP fusion construct can be used for in vivo nuclear and optical imaging of gene transfer.

Mutations in modified virus Ankara protein 183 render it a non-functional counterpart of B14, an inhibitor of nuclear factor kappaB activation.

Vaccinia virus (VACV) encodes multiple proteins to evade host innate immunity, including B14, a virulence factor that binds to the inhibitor of kappaB kinase beta (IKKbeta) and blocks nuclear factor kappaB (NF-kappaB) activation. B14 shares 95 % amino acid identity with the 183 protein encoded by modified virus Ankara (MVA), an attenuated VACV strain being developed as a vaccine vector. To evaluate whether the immunogenicity of MVA might be increased by manipulation of MVA immunomodulatory proteins, the MVA counterpart of B14, protein 183, was characterized. Unlike B14, protein 183 was unstable in eukaryotic cells unless proteasome-mediated protein degradation was inhibited. Furthermore, 183 did not inhibit NF-kappaB activation in response to cytokine stimulation, and did not restore the virulence of VACV strain Western Reserve lacking gene B14R. The instability and non-functionality of 183 are probably explained by a deletion of 6 aa within alpha-helix 6 of the B14 crystal structure.

Vaccinia virus proteins A52 and B14 Share a Bcl-2-like fold but have evolved to inhibit NF-kappaB rather than apoptosis.

Vaccinia virus (VACV), the prototype poxvirus, encodes numerous proteins that modulate the host response to infection. Two such proteins, B14 and A52, act inside infected cells to inhibit activation of NF-kappaB, thereby blocking the production of pro-inflammatory cytokines. We have solved the crystal structures of A52 and B14 at 1.9 A and 2.7 A resolution, respectively. Strikingly, both these proteins adopt a Bcl-2-like fold despite sharing no significant sequence similarity with other viral or cellular Bcl-2-like proteins. Unlike cellular and viral Bcl-2-like proteins described previously, A52 and B14 lack a surface groove for binding BH3 peptides from pro-apoptotic Bcl-2-like proteins and they do not modulate apoptosis. Structure-based phylogenetic analysis of 32 cellular and viral Bcl-2-like protein structures reveals that A52 and B14 are more closely related to each other and to VACV N1 and myxoma virus M11 than they are to other viral or cellular Bcl-2-like proteins. This suggests that a progenitor poxvirus acquired a gene encoding a Bcl-2-like protein and, over the course of evolution, gene duplication events have allowed the virus to exploit this Bcl-2 scaffold for interfering with distinct host signalling pathways.

Inhibition of IkappaB kinase by vaccinia virus virulence factor B14.

The IkappaB kinase (IKK) complex is a key regulator of signal transduction pathways leading to the induction of NF-kappaB-dependent gene expression and production of pro-inflammatory cytokines. It therefore represents a major target for the development of anti-inflammatory therapeutic drugs and may be targeted by pathogens seeking to diminish the host response to infection. Previously, the vaccinia virus (VACV) strain Western Reserve B14 protein was characterised as an intracellular virulence factor that alters the inflammatory response to infection by an unknown mechanism. Here we demonstrate that ectopic expression of B14 inhibited NF-kappaB activation in response to TNFalpha, IL-1beta, poly(I:C), and PMA. In cells infected with VACV lacking gene B14R (vDeltaB14) there was a higher level of phosphorylated IkappaBalpha but a similar level of IkappaBalpha compared to cells infected with control viruses expressing B14, suggesting B14 affects IKK activity. Direct evidence for this was obtained by showing that B14 co-purified and co-precipitated with the endogenous IKK complex from human and mouse cells and inhibited IKK complex enzymatic activity. Notably, the interaction between B14 and the IKK complex required IKKbeta but not IKKalpha, suggesting the interaction occurs via IKKbeta. B14 inhibited NF-kappaB activation induced by overexpression of IKKalpha, IKKbeta, and a constitutively active mutant of IKKalpha, S176/180E, but did not inhibit a comparable mutant of IKKbeta, S177/181E. This suggested that phosphorylation of these serine residues in the activation loop of IKKbeta is targeted by B14, and this was confirmed using Ab specific for phospho-IKKbeta.

Functional and structural studies of the vaccinia virus virulence factor N1 reveal a Bcl-2-like anti-apoptotic protein.

Vaccinia virus (VACV) encodes many immunomodulatory proteins, including inhibitors of apoptosis and modulators of innate immune signalling. VACV protein N1 is an intracellular homodimer that contributes to virus virulence and was reported to inhibit nuclear factor (NF)-kappaB signalling. However, analysis of NF-kappaB signalling in cells infected with recombinant viruses with or without the N1L gene showed no difference in NF-kappaB-dependent gene expression. Given that N1 promotes virus virulence, other possible functions of N1 were investigated and this revealed that N1 is an inhibitor of apoptosis in cells transfected with the N1L gene and in the context of VACV infection. In support of this finding virally expressed N1 co-precipitated with endogenous pro-apoptotic Bcl-2 proteins Bid, Bad and Bax as well as with Bad and Bax expressed by transfection. In addition, the crystal structure of N1 was solved to 2.9 A resolution (0.29 nm). Remarkably, although N1 shows no sequence similarity to cellular proteins, its three-dimensional structure closely resembles Bcl-x(L) and other members of the Bcl-2 protein family. The structure also reveals that N1 has a constitutively open surface groove similar to the grooves of other anti-apoptotic Bcl-2 proteins, which bind the BH3 motifs of pro-apoptotic Bcl-2 family members. Molecular modelling of BH3 peptides into the N1 surface groove, together with analysis of their physico-chemical properties, suggests a mechanism for the specificity of peptide recognition. This study illustrates the importance of the evolutionary conservation of structure, rather than sequence, in protein function and reveals a novel anti-apoptotic protein from orthopoxviruses.