Protein Isoforms and Isozymes

Abstract

Isoforms are highly related gene products that perform essentially the same biological function. Isozymes are isoforms of an enzyme. Isoforms can differ in their biological activity, regulatory properties, temporal and spatial expression, intracellular location or any combination thereof. Isoforms are almost always either the products of one gene or of multiple genes that evolved from a single ancestor gene.

Keywords: evolution; alternative splicing; sorting; gene duplication; gene regulation

Figure 1.

Evolution of isoforms via gene duplication. Duplication will usually produce tandem genes of which one copy can maintain normal established function while another copy is free to accumulate mutations (shown by *) which can change its context of expression. It is argued that the establishment of a changed context of expression provides the driver for further diversification of isoform function.

Figure 2.

Evolution of isoforms via alternative splicing. Generation of additional 5′ terminal, coding or 3′ terminal exons that are alternatively spliced (shown as dotted or filled boxes) allows a single gene to produce its normal transcript plus one or more new transcripts. The original mRNA can maintain established function while the new mRNAs can provide a changed context of expression for the new product. This in turn drives diversification of transcript function.

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Further Reading

Goodnight JA, Mischak H, Kolch W and Mushinski JF (1995) Immunocytochemical localization of eight protein kinase C isozymes over‐expressed in NIH 3T3 fibroblasts. Isoform specific association with microfilaments, Golgi, endoplasmic reticulum and nuclear and cell membranes. Journal of Biological Chemistry 270: 9991–10001.

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Gunning, Peter William(Jan 2006) Protein Isoforms and Isozymes. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0005717]