MESSENGER RIBONUCLEIC-ACID METABOLISM IN MAMMALIAN MITOCHONDRIA .4. DISCRETE POLY(ADENYLIC ACID) LACKING MESSENGER RIBONUCLEIC-ACID SPECIES ASSOCIATED WITH MITOCHONDRIAL POLYSOMES

The mRNA species released from mitochondrial polysomes [Ehrlich ascite hypotetraploid mouse neoplastic cells] prepared by the Mg2+ precipitation technique were further characterized using various analytical techniques. Mitochondrial polysomes were dissociated by treatment with puromycin and chemically labeled with [3H]dimethyl sulfate. About 51% of steady-state mitochondrial mRNA bind to oligo(dT)-cellulose indicating the presence of poly(A) in this fraction. The poly(A)-containing mRNA resolve into discrete bands of 9-16 S.epsilon., while the RNA fraction unable to bind to oligo(dT)-cellulose, representing poly(A)-lacking mRNA, contains 8-12 S.epsilon. species. About 90% of poly(A) lacking RNA hybridizes with mitochondrial DNA and less than 7% hybridizes with nuclear DNA. The extent of hybridization of poly(A)-lacking RNA with mitochondrial DNA was not significantly affected by the presence of excess mitochondrial rRNA, cytoplasmic rRNA, or a 10-fold concentration of poly(A)-containing RNA isolated from total mitochondrial RNA. Possible differences in sequence properties between poly(A)-containing and -lacking mitochondrial mRNA were further verified using a solid phase-bound c[complementary]DNA procedure. Poly(A)-containing mRNA released from mitochondrial polysomes shows over 85% sequence homology with oligo(dT)-cellulose-bound cDNA prepared against total mitochondrial poly(A)-containing RNA. In contrast only about 1% of poly(A)-lacking mitochondrial mRNA hybridizes with the cDNA providing direct evidence for the distinct sequence properties of the 2 mRNA species.