Mammalian mitochondria contain 55S ribosomes of unusual composition and physical-chemical properties. The proposed research will use immunochemical methods to analyze the protein composition of mammalian mitochondrial ribosomes, and to elucidate the biosynthesis, structural organization, and functional roles of several of the proteins of mammalian mitochondrial ribosomes. Mitochondrial ribosomes prepared on a large scale from bovine liver will be used to produce antibodies in rabbits and monoclonal antibodies in mice against subribosomal particles and protein extracts of subribosomal particles. These antibodies will be used in a variety of studies on the biosynthesis, properties and evolution of mammalian mitoribosomal proteins. Antibodies against bovine mt r-proteins will be used to screen human or bovine cDNA expression libraries in lambda gt11, and the cloned DNA inserts obtained will be used to screen bovine or human genomic libraries for the corresponding mt r-protein genes. The cloned cDNA and genomic sequences will be analyzed to determine the sequence, structure and organization of genes for mammalian mitoribosomal proteins. Comparison of the coding sequence with the N-terminal amino acid sequence of the mature r-proteins may reveal N-terminal transit peptides present in precursor r-proteins. Comparison of the human and bovine coding sequences for particular mt r-protein genes should reveal the nature and extent of divergence of these genes, which appear to be evolving more rapidly than those for cytoplasmic r-proteins.