Gene-protein relationships in acetate-requiring mutants of Neurospora crassa deficient in activity of pyruvate dehydrogenase complex.

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Three groups of acetate-requiring mutants of Neurospora crassa, ace-2, ace-3 and ace-4, were found to lack pyruvate dehydrogenase complex (PDHC) activity. Gene-protein relationships in these mutants were investigated. All heterokaryons composed of inter-genic combinations exhibited PDHC activity. In addition, two ace-4 mutants complemented in vivo. On the other hand, in vitro complementation of PDHC activity by simple mixing two extracts was detected only in combinations of ace-2+ace-4 and ace-3+ace-4. Each of the three component enzymes of PDHC was detected as two peaks by Sephadex G-200 gel chromatography. One of them eluted from Sephadex column at void volume comprises high molecular weight aggregate. In the case of the wild-type strain, it may be PDHC itself. The other peak comprises the activity due to free component enzyme. Molecular weights of pyruvate dehydrogenase (PDHase), lipoate acetyltransferase (LATase) and lipoamide reductase (LiRase) in free states were estimated at 190, 000, 300, 000 and 110, 000, respectively. Mutations in ace-4 gene affect LATase not to aggregate to form the core of PDHC. As a result, ace-4 mutants show high activities of free component enzymes, PDHase and LiRase. Mutants of ace-2 and ace-3 genes have the activities of all the three component enzymes of PDHC. Correspondence between ace-2 and ace-3 genes and component enzymes of PDHC could not be determined.
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