Insertional mutagenesis in Neurospora crassa: Cloning and molecular analysis of the preg⁺ gene controlling the activity of the transcriptional activator NUC-1

The transcriptional activator NUC-1 controls the transcription of the genes for phosphorus acquisition enzymes, and its activity is regulated by the negative regulatory factors, PREG and PGOV. In this report, we describe the cloning and molecular analysis of the preg⁺ gene. In Neurospora crassa, as in higher eukaryotes, transformation frequently results in nonhomologous integration of transforming DNA. Insertion of transforming DNA into host genes mutates the gene and provides a molecular tag for cloning it. We obtained two mutants that have an insertion in the preg⁺ and pgov⁺ genes, respectively, among 2 x 10⁵ transformants. The preg⁺ gene was cloned by screening a Neurospora genomic DNA library with DNA sequences flanking the transforming DNA of the rescued plasmid. Northern analysis showed that the transcription of the preg⁺ gene is not regulated by phosphate. The carboxy- terminal half of PREG shows strong homology with Saccharomyces cerevisiae PHO80 whose function is analogous to that of PREG. The preg(c) mutations are located in the well conserved residues which may directly interact with the residues in the regulatory domain of NUC-1.