Abstract
The mitochondrial structure protein (MSP) from 2 maternally inherited, respiratory-deficient mutants of Neurospora (mi-1 and mi-3) differs from wide-type MSP. The MSP from mi-1 has one less tryptophan residue per mole of MSP and one more cysteine residue than does wild-type MSP. The MSP from mi-4 also has one less tryptophan residue, but no other differences have yet been detected in amino-aoid composition. The mutations in mi-2 and mi-3 appear to result from alterations in mitochondrial DNA which in turn result in single amino-acid replacements. Based on the nucleocytoplasmic interactions that are described, which involve protein-protein interactions between malate dehydrogenase and mitochondrial structural protein, an explanation for the pleiotropic phenotype of mi-w and mi-4 is offered.