organization, function, and evolution of gene clusters in eucaryotes

• Published in: The American naturalist Vol. 112; no. 986; pp. 641 - 657
• Main Author: Giles, N.H
• Format: Journal Article
• Language: English
• Published: Salem, Mass University of Chicago Press 01-07-1978
• Subjects: Biosynthesis; Cell aggregates; Enzymes; Evolution; Evolutionary genetics; Fungi; Molecular genetics; Multigene family; Neurospora; Neurospora crassa
• ISSN: 0003-0147; 1537-5323
• DOI: 10.1086/283306

Present genetic and biochemical evidence suggests that two basic types of gene clusters occur in eucalypts. The first type encodes an enzyme aggregate (multienzyme complex). In an increasing number of instances, such gene clusters have been shown to be cluster-genes, i.e., single genes encoding multifunctional polypeptide chains, typically associated as homopolymeric aggregates. In several instances, evidence supports a channeling role for such enzyme aggregates, i.e., the aggregate serves to sequester intermediates in a particular biochemical pathway and to prevent competition between two potential competitive pathways. Gene clusters are considered to have evolved by retroevolution involving successive tandem gene duplications followed by functional divergence. Apparently, natural selection has often resulted in the further evolution of such gene clusters into cluster-genes by the process of gene fusion, especially in eucaryotes. The second (and apparently less frequent) type of gene cluster in eucaryotes is a true cluster of contiguous but separate genes which do not encode an enzyme aggregate. Certain of these clusters appear to have operon-like characteristics. However, in the absence of evidence for polycistronic mRNA production, at least one of these clusters (the qa cluster in Neurospora) appears to be maintained by natural selection because it contains a gene encoding a regulatory protein which is primarily cis acting.