The messenger-like properties of the poly(A) + RNA in mammalian mitochondria

Abstract

This is the first demonstration that the poly(A)-containing RNA from mammalian mitochondria behaves like messenger RNA in mitochondrial specific protein synthesis. The mitochondrial RNA in HeLa cells is selectively labeled in the presence of camptothecin, the mitochondria isolated, lysed with weak detergents, and the mitochondrial contents sedimented in sucrose gradients. Much of the poly(A)-containing RNA sediments rapidly with polyribosome-like structures. Most important, the association of the poly(A) + RNA with heavy structures is disrupted quantitatively by puromycin, which should be selective for RNA engaged in protein synthesis. The disaggregation by puromycin is largely prevented by the simultaneous addition of chloramphenicol, which demonstrates association with mitochondrial protein synthesis. A minimum lifetime is estimated for mitochondrial RNA of from 1 1 2 –2 hr . This decay rate is observed after the block of new synthesis with either actinomycin or cordycepin. The decay of the poly(A) + RNA is faster than that of mitochondrial poly(A) −. The decay in ethidium bromide is much more rapid and constitutes additional evidence that ethidium has an overall deleterious effect on mitochondrial integrity. The lifetimes observed are long compared to the transcription time. In this sense, the mitochondrial messenger-like RNA more closely resembles eucaryotic rather than procaryotic mRNA.