Comparison of identified vs. unidentified proteins for (A)Helicobacter pylori, (B) Pyrococcus abyssi, (C) Methanococcus jannaschii, and (D)Drosophila melanogaster. Dashed lines represent proteins identified, possibly on the basis of homology; solid lines represent proteins for which no function has been identified (unannotated proteins in the D. melanogaster database and proteins annotated as hypothetical in the other three databases).