The imported mitochondrial ribosomal proteins of the fungus Neurospora crassa and their nuclear genes will be used as a model system for study of the structure-function relationships of eukaryotic genes, in particular the mechanisms for nuclear-mitochondrial interaction and the mechanisms for coordinate control of specialized classes of genes. Antibodies against mitochondrial ribosomal proteins will be produced and used for immunoprecipitation of the newly synthesized proteins to determine (1) whether they are made as longer precursors, (2) whether they share a common import pathway, and (3) whether their production is coordinately increased in response to inhibition of mitochondrial function. Messenger RNAs enriched for species coding these ribosomal proteins will be isolated and used to identify the genes in a Neurospora clone bank. The organization of the genes will be investigated and their structures analyzed and compared to study the molecular basis of their import and control. The cloned genes will be used to identify and quantitate in vivo transcription products to dissect the processes involved in the response of these genes to a physiological stimulus.