Mitochondrial biogenesis requires the coordinate expression of their nuclear and mitochondrial genomes. The long term goal of this research is to understand the nature of the controlling signals in the Saccharomyces cerevisiae that synchronize the production of mitochondrial proteins encoded in the separate compartments. The characterization of nuclear respiratory deficient pet mutants has identified several genes necessary for processing of mitochondrial precursor transcripts and translation of the resultant mRNAs on mitochondrial ribosomes. One group of pet mutants describes the nuclear gene CBP1, which encodes a 76,500 dalton protein that is imported into the organelle and interacts with the 5' end of the cytochrome b precursor RNA. It is planned to purify the CBP1 protein and study the interaction with substrate RNA in vitro. The CBP1 gene produces two polyA+ mRNAs, differing at the 3' end by 900 nucleotides. How and why the abundance of the RNAs is regulated by glucose repression will be investigated. A coding sequence terminates in the TATAA box for CBP1. This upstream gene is expressed as a 1.1 kb mRNA that is also under catabolite control. Deletions of this gene lead to a phenotype similar to deletion of a mitochondrial outer membrane protein gene. The sequence of the gene, will be determined. Does transcription of this gene affect expression of CBP1 and define how does the encoded protein function in the cell. At the present time we have only a sketchy understanding of how the functional integrity of subcellular organelles is maintained and modulated in response to a changing environment. In yeast the production of mitochondrial respiratory-chain components are significantly altered by changing their growth conditions. As three of the large enzyme complexes of the inner mitochondrine membrane are composed of subunits encoded both on nuclear chromosomes and on the organella genome, the change of expression due to media availability must be coordinated. Is it transcriptional or translational factors that enhance and decrease production of nuclearly encoded respiratory chain components? The answer to this question is of great importance for an understanding of mitochondrial respiration.
