No abstract

No abstract

No abstract

No abstract

One approach to an understanding of the nature of extrachromosomal heredity, subeellular morphology, and nucleocytoplasmic relationships is through the investigation of the genetics of enzymes and proteins of mitochondria. Genetic information for the primary structure of some mitochondrial-localized enzymes resides in nuclear DNA;' 2 no direct demonstration of a gene-protein relationship involving mitochondrial DNA has been previously reported.Concepts developed in several areas of independent investigation led to the working hypothesis of this study. First, although concepts of extrachromosomal heredity have been evolving for many years, only one class of extrachromosomal mutations affecting mitochondria are well known; these are the respiratory-deficient mutants of yeast and Neurospora.3 Extensive analyses of such mutants have not produced results interpretable in terms of either the classical one gene-one enzyme hypothesis or related corollaries regarding pathways of intermediary metabolism. Rather, several of the components of the electron transport chain are found to occur in either excess or deficit in those mutants. In addition, Green and associates4 have proposed that polymacromolecular assemblies called elementary particles, with a fixed set of proteins in invariant proportions, are associated with the mitochondrial inner membrane. Among the principal components of those particles are the enzymes of the electron transport system and the mitochondrial structural protein. The importance of the structural protein is emphasized not only by its quantitative preponderance in the mitochondria, but also by its critical role in the organization and assembly of the enzymes of the particles. Moreover, recent investigations indicate that mitochrondria from all organisms contain DNA.' That this DNA may play a hereditary role is indicated by observations that Neurospora mitochondria replicate by division of pre-existing Inlitochondria6 and exhibit genetic continuity after interhyphal transplantation.7In this communication, the results of experiments stimulated by the foregoing concepts support the hypothesis that two different extrachromosomal mutations of (presumably) mitochondrial DNA lead to alterations of the primary structure