To reveal the WY 14643 presence of signalogs in current orthology-based prediction databases, we compared already identified BEZ235 PI3K inhibitor interologs in worms, flies, and humans using 3 species-specific datasets with interologs generated from SignaLink data. Neither SignaLink nor the current signalog identification approach identify interologs directly, thus we used an indirect method. First, we deduced interologs from SignaLink data by linking two proteins in an organism, if their orthologs interact in at least one other of the three organisms. After generating all possible interologs from SignaLink, we examined only those interologs in which at least one of the interactors is a signalog protein. To examine the novelty of the predicted signaling roles and to quantify their confidence levels, we first classified these predicted proteins into 5 groups on the basis of their known properties. These groups range from genes for which only the ORF is known to genes whose protein products have known molecular function. In each of the three organisms examined, we found only one protein already known as a signaling pathway component; for these three proteins we predicted additional pathway annotations. In C. elegans and D. melanogaster, most signalogs have not yet been characterized biochemically, while in humans, only 26% of the signalogs remain uncharacterized. Note that this lower rate is partly due to the larger abundance of literature information on signaling in humans compared to worms and flies. Taken together, we conclude that signalog prediction can effectively contribute to the identification of novel signaling components. Finally, to reveal the presence of signalogs in current orthologybased prediction databases, we used interologs. We compared the interologs generated for this test from the SignaLink dataset with the interologs listed for worms, flies and humans by 3 species-specific databases. We examined only those interologs, where at least one of the interactors is a signalog protein. We found that in worms, flies and humans, respectively 34, 30, and 48 signalogs are present only in the SignaLink dataset,indicating that a high portion of the predicted proteins has not yet been investigated by this orthology based prediction method. Altogether, in SignaLink and in the 3 species-specific resources, we found 1028, 1338, and 465 interologs in worms, flies and humans, respectively. The overlap between interologs generated from SignaLink and the interologs from any of the other 3 databases was relatively low: 5.5% in worms, 38.8% in flies and 12.5% in humans. Shared interologs can be interpreted as already known orthology-based predictions. A low number of overlapping interologs suggests that most of our current signalog predictions are novel.