Molecular control of copper homeostasis in filamentous fungi: increased expression of a metallothionein gene during aging of Podospora anserina

The lifespan of the ascomycete Podospora anserina was previously demonstrat ed to be significantly increased in a copper-uptake mutant, suggesting that copper is a potential stressor involved in degenerative processes. In orde r to determine whether changes in copper stress occur in the cells during n ormal aging of cultures, we cloned and characterized a gene coding for a co mponent of the molecular machinery involved in the control of copper homeos tasis. This gene, PaMt1, is a single-copy gene that encodes a metallothione in of 26 amino acids. The coding sequence of PaMt1 is interrupted by a sing le intron. The deduced amino acid sequence shows a high degree of sequence identity to metallothioneins of the filamentous ascomycete Neurospora crass a and the basidiomycete Agaricus bisporus, and to the N-terminal portion of mammalian metallothioneins. Levels of PaMt1 transcript increase in respons e to elevated amounts of copper in the growth medium and during aging of wi ld-type cultures. In contrast, in the long-lived mutant grisea, transcript levels first increase but then decrease again. The ability of wild-type cul tures to respond to exogenous copper stress via the induction of PaMt1 tran scription is not affected as they grow older.