MOLECULAR CHARACTERIZATION OF THE QA-4 GENE OF NEUROSPORA-CRASSA

The qa-4 gene of N. crassa encodes 3-dehydroshikimate dehydratase, which catalyzes the third step of the quinic acid (qa) catabolic pathway. The enzyme was previously purified and characterized as a monomer of .apprx. 37 kilodaltons. The nucleotide sequence of the qa-4 gene is presented 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, 3 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 20 previously isolated qa-4 mutants revealed that 2 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.