Expression distributions of mouse proteins. (a) Expression pattern of all mapped proteins expressed in at least a single tissue (5,528 out of 6,242 proteins). (b) Expression pattern of proteins in different functional groups and (c) in different phyletic groups. The plot presents the fraction of proteins in a group that are expressed in N tissues. The analysis is restricted to those proteins expressed in at least a single tissue. Sample size (number of assigned proteins): 1,294 enzymes; 343 transporters; 450 signal transduction; 214 transcription regulation; 1,359 universal; 1,951 eukaryote-specific; 1,281 metazoan-specific; and 910 mammalian-specific.