Mitochondrial translation products

Including the rate of proteolysis of mitochondrial translation products (48), dlhydrollpoate-lnduced ATP synthesis In promltochondrla (49), mitochondrial proliferation (50) and release from glucose repression (51). The A-9 Isomer was the most efficient of the cls-octadecenolc acid compounds evaluated In this latter study, with elcosaenolc acid supporting 15% of the release Induced by oleic acid. All of the listed processes were Inhibited by saturated fatty acids. 

Limits on Mitochondrial Translational Products and Their Specification and Function... 

Does an Authentic Mitochondrial Translational Product Contain fMet ... 

We first became aware of the possibility that continued translation by the intramitochondrial system of protein synthesis might be contingent on the operations of the cytoribosomal system by the discovery that effective synthesis of cytochrome oxidase could be inhibited, not only by CAP, but also by CHX. This particular effect we now know to be due to the fact that this enzyme complex actually contains two classes of polypeptides synthesized by the two systems (see Sections 2.1.1 and 2.3.1). However, upon exploring the use of formate as a tag for mitochondrial translational products (Section 2.2.1), we met with very similar, and equally puzzling, observations. Now it was the incorporation of labeled formate into membrane proteins that appeared to be equally sensitive to both these in-... 

How then can one reconcile these observations with the well-authenticated instance of CHX-insensitive protein synthesis in and by mitochondria, measured either directly or, more commonly, as the CAP-sensitive component of incorporation of labeled precursors in the presence of CHX (see, e.g., refs. 6, 9, 94) We believe that these differences can be explained by the actual experimental conditions employed our studies have been designed to deal with the steady-state conditions present in exponentially growing cells, while the studies employing CHX for the identification of mitochondrial translational products use nongrowing cells at a very high cell density or undergoing derepression, or both. In partial confirmation of this hypothesis we have found that, with a number of different strains, the conditions reported in the literature as being optimal for the extensive incorporation of amino acids in the presense of CHX lead to very poor incorporation of formate, while conditions that permit extensive incorporation of formate are not particularly favorable for CHX-insensitive amino acid incorporation. 

From labeling experiments II and IV (Table I, Figs. 7B and D), the following conclusion can be drawn The three large cytochrome oxidase subunits are mitochondrial translation products their labeling is insensitive to cycloheximide, but is sensitive to chloramphenicol. The four small cytochrome oxidase subunits are cytoplasmic translation products their labeling is sensitive to cycloheximide, but is insensitive to chloramphenicol. 

It was of interest to determine the effects of the petite-inducing conditions described above on mitochondrial inner-membrane proteins, and, in particular, on products of mitochondrial protein synthesis. The efficient and quantitative production of petites at 18°C affords a special opportunity to examine the fate of mitochondrial translation products during the course... 

The necessity of mitochondrial translation products for stability of the mitochondrial genome can be visualized either as a direct requirement—for... 

There is now considerable evidence indicating a close interdependence between cytoplasmic- and mitoribosomal-directed proteins for the assembly and function of inner-membrane complexes like cytochrome oxidase and the oligomycin-sensitive ATPase. Thus an alteration in a nuclear gene product could profoundly affect the level or functioning of a mitochondrial translation product or products such a situation could apply as well to the replication of wild-type mtDNA. 

In terms of both the relative amounts and the total extent of synthesis of mitochondrial translation products, promitochondria do not differ much from mitochondria in fully derepressed cells. In order to determine if the... 

Less than a dozen or so polypeptides are synthesized on mitochondrial ribosomes, accounting for 5-1.5% of the mitochondrial protein. Three of the polypeptides have been identified as components of cytochrome oxi-dase, four are associated with oligomycin-sensitive ATPase, " and one is a component of cytochrome fc. It is not known at this time whether these mitochondrial translation products are structural or catalytic components of these inner-membrane complexes. 

Douglas MG and Butow RA (1976) Variant forms of mitochondrial translation products in yeasts evidence for location of determinants on mitochondrial DNA, Proc. Natl. Acad. Sci. U.S.A. 73, 1083-1086. 

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