How Many Phenotypes From One Genotype? The Case of Prion Diseases

✍ Scribed by Henrik Kacser; J.Rankin Small

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 198 KB
• Volume: 182
• Category: Article
• ISSN: 0022-5193
• DOI: 10.1006/jtbi.1996.0157

✦ Synopsis

The usual assumption, namely that the underlying biochemical reactions in an organism tend to a unique steady-state, is shown to be not always correct. There are certain pathway mechanisms (e.g. positive feedback) which allow the system to exists in two alternative stable steady states. This bistability implies that environmental perturbations can "switch" the system from either state to the other. Such a switch takes place at the metabolic level and hence a single genotype can display two different, alternative, phenotypes without involving any changes in gene expression. The infective transmission of Scrapie-type diseases is explained here by such a mechanism involving protein-only changes.

7 1996 Academic Press Limited F. 2. The evolution of the uniquely stable system towards a steady state. (A, • • • •; B, ---; C, -). Two initial concentrations of the three metabolites are used. (a) 1 × 10 -6 units; (b) 3.0 units. In both cases the same steady-state values (see Table 1) are being approached asymptotically.