CHAPTER 7 - Gene Clusters and the Regulation of Biosynthetic Pathways in Fungi

Abstract

This chapter describes gene clusters and the regulation of biosynthetic pathways in fungi. Bacterial gene clusters are organized into a suprafunctional unit, the operon. A distinctive feature of these fungal clusters is that the enzymes specified by the contiguous genes remain physically associated. It is not yet known whether the messenger RNA transcribed from these gene clusters has internal termination and initiation signals and, therefore, whether translation of the message yields more than a single polypeptide chain. Some evidence suggests that the importance of fungal gene clusters is their role in the production of enzyme aggregates. Even if enzyme complexes are important in the regulation of the biosynthesis of amino acids in fungi, it is not clear why the genes specifying the components of the aggregate should be clustered. In several respects, each of the clusters discussed has the appearance of a fused gene specifying a single multifunctional protein. The protein gives the appearance of having the individual catalytic activities arranged in a linear array along the length of the molecule, collinear with the genetic map. By analogy, proteolytic cleavage and refolding may be an important step in the concatenation of events that allow aggregates in fungi to assume their final mature and active state. This kind of role for proteolytic cleavage has been verified in the case of insulin.