Molecular analysis of the Neurospora qa-1 regulatory region indicates that two interacting genes control qa gene expression.

The qa-1 regulatory region controls the expression of the three structural genes required for the early reactions in quinic acid catabolism in Neurospora crassa. Genetic analysis previously identified two types of noninducible qa-1 mutants, qa-1S and qa-1F, which mapped in separate non-overlapping regions. These mutations were originally interpreted as defining separate domains of a single regulatory protein. This communication describes the further genetic and physical characterization of the qa-1 regulatory region. Using both Neurospora transformation and DNA . RNA hybridization, it has been shown that the qa-1 region consists of two distinct genes corresponding to the two original mutational types qa-1S and qa-1F. The analysis of the mRNA species hybridizing to these regions indicates that the qa-1F gene encodes a 2.9-kilobase (kb) mRNA, while the qa-1S gene encodes related 4.1-kb and 3.4-kb mRNAs. The transcriptional regulation of one of these genes, qa-1S, was examined. Evidence is presented that the qa-1S gene is induced by quinic acid and is also subject to apparent autogenous regulation as well as to control by the qa-1F gene product. Based on these results and earlier genetic analysis, the hypothesis is proposed that one of the two qa regulatory genes encodes a repressor protein (qa-1S), and the other encodes an activator protein (qa-1F), both of which control qa gene expression.