Functional genomics studied by proteomics.

The human genome contains about 30,000 genes, each creating several transcripts per gene. Transcript structures and expression are studied by high-throughput transcriptomic techniques using microarrays. Generally, transcripts are not directly operating molecules, but are translated into functional proteins, post-translationally modified by proteolysis, glycosylation, phosphorylation, etc., sometimes with great functional impact. Proteins need to be analyzed by proteomic techniques, less suited for high-throughput. Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), separating thousands of proteins has developed slowly over the past quarter of a century. This technique is now quite reproducible and suitable for differential proteomics, comparing normal and diseased cells/tissues revealing differentially regulated proteins. 2D-PAGE is combined with protein-identification methods, currently mass spectrometry (MS), which has been significantly improved over the last decade. Other proteomic techniques studying protein-protein interactions are now either established or still being developed, such as peptide or protein arrays, phage display, and the yeast two-hybrid system. The strengths and weaknesses of these techniques are discussed.