Repression of the branched-chain amino acid biosynthetic enzymes in developing conidia and mycelia of Neurospora.

Abstract

During germination of the conidia of wild type Neurospora crassa, the enzymes of the isoleucine–valine pathway increase in activity. This increase is partially repressed in the presence of a combination of exogenous isoleucine, leucine, and valine. Repressed levels of enzymic activity are also observed in mycelium during the logarithmic phase of growth. In both cases, isoleucine and leucine together are almost as effective without valine as when the three are present together. The synthesis of these enzymes does appear to be affected by their end products but not to the extent exhibited in bacteria.