The qa-4 gene of Neurospora crassa encodes 3-dehydroshikimate dehydratase, which catalyzes the third step of the quinic acid (qa) catabolic pathway. The enzyme has previously been purified and characterized as a monomer of approx. 37 kDal. The nucleotide sequence of the qa-4 gene is presented here and the amino acid composition and tentative NH2-terminal sequence confirm the identification of the coding region within the qa-4 DNA sequence. There are no introns in the qa-4 coding region. By S1 nuclease mapping and primer extension analysis three distinct regions of transcription initiation were identified. Heterogeneity was also observed in the 3' ends of qa-4 mRNA. 5' and 3' untranslated regions of the qa-4 gene were compared with the corresponding regions in other Neurospora genes. Genomic blot analysis of twenty previously isolated qa-4 mutants revealed that two mutants, MC150 and MC191, have restriction patterns altered from wild type. In each strain the alteration occurs in the 3' half of the qa-4 coding region.