THE 59-KDA POLYPEPTIDE CONSTITUENT OF 8-10-NM CYTOPLASMIC FILAMENTS IN NEUROSPORA-CRASSA IS A PYRUVATE DECARBOXYLASE

The fungus Neurospora crassa harbors large amounts of cytoplasmic fila ments which are homopolymers of a 59-kDa polypeptide (P59Nc). We have used molecular cloning, sequencing and enzyme activity measurement str ategies to demonstrate that these filaments are made of pyruvate decar boxylase (PDC, EC 4.1.1.1), which is the key enzyme in the glycolytic- fermentative pathway of ethanol production in fungi, and in certain pl ants and bacteria. Immunofluorescence analyses of 8-10-nm filaments, a s well as quantitative Northern blot studies of P59Nc mRNA and measure ments of PDC activity, showed that the presence and abundance of PDC f ilaments depends on the metabolic growth conditions of the cells. Thes e findings may be of relevance to the biology of ethanol production by fungi, and may shed light on the nature and variable presence of fila ment bundles described in fungal cells.