Progression from genome to proteome. When a gene is expressed, the coding DNA strand is transcribed into an mRNA, which is edited by intron excision and the joining of exons. At the transcriptome level, the study of mRNA expression by a genome at a given time is routinely performed using microarray analysis.89 Proteins are synthesized and may undergo cotranslational and posttranslational modification processes that are often involved in the formation of the functionally active structure of the protein. A given mRNA sequence can give rise to more than one protein. This figure illustrates aspects of this process. Although some of the observed properties of an organism can be correlated with the activity of a single gene, most of the time these are determined by the joint action of many gene products. It is only at the proteome level that the gene exerts its “function.” The operation and the functions of a living cell are usually the result of proteome dynamics. Protein-protein interactions are often responsible for the regulation of cellular metabolism (enzymes), maintenance of architectural features (structural proteins), and transfer and processing of information (signal and regulatory proteins). Because proteome analysis provides a view of the biologic processes at their level of occurrence, proteomics offers a better understanding than genomics of cell cycle, cell death, development stage, cell function, and cellular responses to external stimuli and disease. Proteomics has become an important step in the development and validation of diagnostics and therapeutics.90
