The imported mitochondrial ribosomal proteins of the fungus Neurospora crassa and their nuclear genes are being 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 produced against mitochondrial ribosomal proteins have been used in immune assays to identify thirteen positive clones generated by incorporating N. crassa complimentary DNA into a bacteriophage lambda expression vector. The thirteen putative mitochondrial ribosomal protein clones have been sorted into classes by hybridization to restriction fragments of N. crassa genomic DNA. By this criterion, the cDNA clones represent at least four different genes. These cDNA clones are being characterized by sequence analysis and are also being used as probes to identify corresponding clones from a bank of genomic DNA fragments. Characterization of these clones will help to determine whether these genes contain protein transport leader sequences directing the proteins to the mitochondrion, whether the genes contain introns like yeast cytoplasmic ribosomal protein genes, and whether the genes show any indication of being clustered in the nuclear genome. The cloned genes will also be used to select and study messenger RNAs for these imported proteins and to characterize the control of expression of their genes. They will be used to study coordination of expression of the genes and to investigate the transcriptional response of these genes to different physiological conditions and to inhibitors of mitochondrial function. Antigenic fusion proteins produced by these cDNA clones are being used to generate monoclonal antibodies. If the clones have been correctly identified, the resultant monoclonal antibodies should react specifically with individual mitochondrial ribosomal proteins. These antibodies will be used to correlate the cloned genes with specific ribosomal proteins. They will also be used to study biosynthesis of the proteins: precursor forms (if any), mitochondrial import, and processing.