NAD-SPECIFIC GLUTAMATE-DEHYDROGENASE OF NEUROSPORA-CRASSA - CLONING, COMPLETE NUCLEOTIDE-SEQUENCE, AND GENE-MAPPING()

The NAD+-specific glutamate dehydrogenase (NAD-GDH) of the filamentous fungus Neurospora crassa is a tetrameric enzyme, regulated by catabol ite repression. The amino acid sequence of this enzyme had been publis hed several years ago. With the object of investigating the molecular mechanism of catabolite repression, the nucleotide sequence of genomic clones containing the coding region, along with 5'- and 3'-flanking n oncoding segments of the NAD-GDH transcription unit, was obtained. The gdh structural gene was shown to code for a polypeptide of 1047 resid ues, with a calculated molecular mass of 118 280 daltons. The coding s equence is interrupted by two short introns located close to the N- an d C-terminal domains of the polypeptide. Consensus intron boundaries a nd internal splice sequences resemble closely those of other N. crassa genes. A comparison of the amino acid sequence deduced from the nucle otide sequence with the previously published sequence showed several d iscrepancies between the two. Nucleotide sequence corresponding to a g ap in the amino acid sequence was located in the genomic clone. Geneti c mapping by restriction fragment length polymorphism analysis localiz ed the gdh gene close to the loci trp-1 and con-7 on the right arm of linkage group III.