Title:
The Nitrogen Regulatory Circuit of the Filamentous Fungi, Neurospora and Aspergillus
Speaker:
George A. Marzluf, Department of Biochemistry, The Ohio State University
Subject:
Quantitative Mathematical Modeling of Gene Regulatory Networks
Area:
Medicine
Type of school:
university
School name:
ohio state university
Country:
United States
Course language:
English
Course media:
Video
Course duration:
Contributor:
pbp
Comments:
Author: George A. Marzluf, Department of Biochemistry, The Ohio State University
Title: The Nitrogen Regulatory Circuit of the Filamentous Fungi, Neurospora and Aspergillus
Streaming Video: Real Media
The filamentous fungi, Neurospora crassa and Aspergillus nidulans, utilize ammonia, glutamine or glutamate as nitrogen sources preferentially, but when these favored sources are not available, they are capable of using many other secondary nitrogen-containing compounds, such as purines, nitrate, amino acids and proteins. Nitrogen repression prevents the expression of the spectrum of genes encoding enzymes for catabolism of secondary nitrogen sources. Repression occurs by glutamine but the identity of the element which actually senses this metabolite remains unknown. Upon conditions of derepression, the expression of an entire set of structural genes which allow catabolism of many varied alternative nitrogen sources is controlled by a complex regulatory circuit. The synthesis of the permeases and enzymes of a particular catabolic pathway often requires two distinct positive signals: First, a global signal indicating nitrotgen derepression, and second, a pathway-specific signal which indicates the presence of a substrate or intermediate of the pathway. This two-step requirement permits the selective expression of just the enzymes of a specific catabolic pathway. Positive-acting global nitrogen regulatory proteins, NIT2 in Neurospora and AREA in Aspergillus, are GATA factors, DNA binding proteins which possess a single Cys2/Cys2 zinc finger. A negative-acting protein, NMR, binds to two regions of NIT2, preventing its function during conditions of nitrogen repression. Although similar, significant differences occur in the mechanism by which NIT2 and AREA control gene expression. The utilization of inorganic nitrate requires the presence of a pathway-specific factor, NIT4 in Neurospora, a DNA binding protein with a Gal4-like Cys6/Zn2 motif. Optimal expression of ni