Isolation and regulation of expression of the Neurospora crassa copper metallothionein gene.

The N. crassa CuMT gene has been cloned and its nucleotide sequence determined. To this end an MT specific undecanucleotide was synthesized and used for cDNA synthesis with enriched MT mRNA as a template. Sequence analysis of the cDNA obtained allowed the synthesis of a unique 21mer which was used as a hybridization probe to screen a genomic DNA library of N. crassa. Several positive clones were isolated and subjected to restriction and sequence analysis. In agreement with the published amino acid sequence, the gene codes for a polypeptide of 26 amino acid residues in length. The coding region is interrupted by a small intron. Compared to the structure of mammalian MT genes the intron-exon boundaries are located in different sequence positions. The induction of MT mRNA was studied by Northern analysis. Maximum levels of MT mRNA were detected about 1 hour after addition of copper ions to mycelium of N. crassa. The half-life time of the messenger was estimated as 2.5 hours. The CuMT amounts reach a maximum level at 3 hours after induction and thereafter remain constant.