Evolution
It is thought that early in evolution the trpB2 gene was duplicated. One copy entered the trp operon as trpB2i allowing for its expression with trpA. TrpB2i formed transient complexes with TrpA and in the process activated TrpA unidirectionally. The other copy remained outside as trpB2o, and fulfilled an existing role or played a new one such as acting as a salvage protein for indole. TrpB2i evolved into TrpB1, which formed permanent complexes with trpA resulting in bidirectional activation. The advantage of the indole salvage protein declined and the TrpB gene was lost. Finally, the TrpB1 and TrpA genes were fused resulting in the formation the bifunctional enzyme.
Read more about this topic: Tryptophan Synthase
Famous quotes containing the word evolution:
“The more specific idea of evolution now reached is—a change from an indefinite, incoherent homogeneity to a definite, coherent heterogeneity, accompanying the dissipation of motion and integration of matter.”
—Herbert Spencer (1820–1903)
“As a natural process, of the same character as the development of a tree from its seed, or of a fowl from its egg, evolution excludes creation and all other kinds of supernatural intervention.”
—Thomas Henry Huxley (1825–95)
“The more specific idea of evolution now reached is—a change from an indefinite, incoherent homogeneity to a definite, coherent heterogeneity, accompanying the dissipation of motion and integration of matter.”
—Herbert Spencer (1820–1903)