DroID (http://droidb.org/), the Drosophila Interactions Database, is a comprehensive public resource for Drosophila gene and protein interactions. DroID contains genetic interactions and experimentally detected protein–protein interactions curated from the literature and from external databases, and predicted protein interactions based on experiments in other species. Protein interactions are annotated with experimental details and periodically updated confidence scores. Data in DroID is accessible through user-friendly, intuitive interfaces that allow simple or advanced searches and graphical visualization of interaction networks. DroID has been expanded to include interaction types that enable more complete analyses of the genetic networks that underlie biological processes. In addition to protein–protein and genetic interactions, the database now includes transcription factor–gene and regulatory RNA–gene interactions. In addition, DroID now has more gene expression data that can be used to search and filter interaction networks. Orthologous gene mappings of Drosophila genes to other organisms are also available to facilitate finding interactions based on gene names and identifiers for a number of common model organisms and humans. Improvements have been made to the web and graphical interfaces to help biologists gain a comprehensive view of the interaction networks relevant to the genes and systems that they study.

Translation initiation of the picornavirus genome is regulated by an internal ribosome entry site (IRES). The IRES of a neurovirulent picornavirus, the GDVII strain of Theiler's murine encephalomyelitis virus, requires polypyrimidine tract-binding protein (PTB) for its function. Although neural cells are de®cient in PTB, they express a neural-speci®c homologue of PTB (nPTB). We now show that nPTB and PTB bind similarly to multiple sites in the GDVII IRES, rendering it competent for ef®cient translation initiation. Mutation of a PTB or nPTB site results in a more prominent decrease in nPTB than PTB binding, a decrease in activity of nPTB compared with PTB in promoting translation initiation, and attenuation of the neurovirulence of the virus without a marked effect on virus growth in non-neural cells. The addition of a secondsite mutation in the mutant IRES generates a new PTB (nPTB) binding site, and restores nPTB binding, translation initiation and neurovirulence. We conclude that the tissue-speci®c expression and differential RNA-binding properties of PTB and nPTB are important determinants of cell-speci®c translational control and viral neurovirulence.

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Mutations critical for the central nervous system (CNS) attenuation of the Sabin vaccine strains of poliovirus (PV) are located within the viral internal ribosome entry site (IRES).We examined the interaction of the IRESs of PV type 3 (PV3) and Sabin type 3 (Sabin3) with polypyrimidine tract-binding protein (PTB) and a neural cell-specific homologue, nPTB. PTB and nPTB were found to bind to a site directly adjacent to the attenuating mutation, and binding at this site was less efficient on the Sabin3 IRES than on the PV3 IRES. Translation mediated by the PV3 and Sabin3 IRESs in neurons of the chicken embryo spinal cord demonstrated a translation deficit for the Sabin3 IRES that could be rescued by increasing PTB expression in the CNS. These data suggest that the low levels of PTB available in the CNS, coupled to a reduced binding of PTB on the Sabin3 IRES, leads to its CNS-specific attenuation. This study also demonstrates the use of the chicken embryo to easily investigate translation of RNA within a neuron in the CNS of an intact living organism.Poliovirus (PV) infection worldwide has been successfully controlled through the use of two highly effective vaccines. The first, developed by Salk and colleagues, was prepared by formalin treatment of strains from the three major serotypes of PV to generate a killed-virus vaccine. The second, a live, attenuated virus vaccine developed by Sabin and colleagues, was prepared by serial passage of the three major PV strains in nonhuman primates and in cultured primate cells until strains with reduced neurovirulence were obtained (46). These Sabin strains are significantly attenuated in the central nervous system (CNS) but replicate at wild-type (WT) levels in the gut; similarly, these strains do not grow as well in cultured neuroblastoma cells as they do in cultured HeLa cells (25,26). The Sabin strains are therefore considered to have a neural cellspecific attenuation.PV has a single-stranded, positive-sense RNA genome of greater than 7,500 nucleotides (nt). An internal ribosome entry site (IRES) located in the 5Ј untranslated region (UTR) of the picornavirus RNA genome mediates efficient translation initiation of the viral polyprotein (reviewed in references 18 and 41). Studies of recombinant PVs made between attenuated vaccine strains and their neurovirulent progenitors have shown that a major determinant of neuroattenuation maps to a single point mutation located within the viral IRES at nt 480, 481, or 472 in the case of Sabin type 1 (Sabin1), Sabin2, and Sabin3, respectively (21,35,49). In addition, the Sabin3 vaccine strain has been found to revert in humans to neurovirulence, and this reversion is associated with a mutation that restores the WT sequence at nt 472 (6). Studies have demonstrated a translational deficiency of the Sabin3 IRES in Krebs-2 cells and neuroblastoma cells that is not present in HeLa cells (26,47,48). These findings have led to the proposal that the attenuating point mutation located in the IRES of the Sabin vaccine strains inhibits IRES-medi...