Davidson J N, Chen K C, Jamison R S, Musmanno L A, Kern C B
Department of Microbiology and Immunology, University of Kentucky, Lexington 40536-0084.
Bioessays. 1993 Mar;15(3):157-64. doi: 10.1002/bies.950150303.
Some metabolic pathways are nearly ubiquitous among organisms: the genes encoding the enzymes for such pathways must therefore be ancient and essential. De novo pyrimidine biosynthesis is an example of one such metabolic pathway. In animals a single protein called CAD carries the first three steps of this pathway. The same three enzymes in prokaryotes are associated with separate proteins. The CAD gene appears to have evolved through a process of gene duplication and DNA rearrangement, leading to an in-frame gene fusion encoding a chimeric protein. A driving force for the creation of eukaryotic genes encoding multienzymatic proteins such as CAD may be the advantage of coordinate expression of enzymes catalyzing steps in a biosynthetic pathway. The analogous structure in bacteria is the operon. Differences in the translational mechanisms of eukaryotes and prokaryotes may have dictated the different strategies used by organisms to evolve coordinately regulated genes.
因此，编码此类途径中酶的基因必定古老且至关重要。从头嘧啶生物合成就是这样一种代谢途径的例子。在动物中，一种名为CAD的单一蛋白质负责该途径的前三个步骤。原核生物中的这三种酶与不同的蛋白质相关联。CAD基因似乎是通过基因复制和DNA重排过程进化而来的，导致了一个编码嵌合蛋白的读框内基因融合。创建像CAD这样编码多酶蛋白的真核基因的驱动力可能是催化生物合成途径中各个步骤的酶协同表达的优势。细菌中的类似结构是操纵子。真核生物和原核生物翻译机制的差异可能决定了生物体进化出协同调控基因所采用的不同策略。
