Expression of the mitochondrial genome in HeLa cells. X. Properties of mitochondrial polysomes |
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| Authors: | D Ojala G Attardi |
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| Affiliation: | 1. School of Metallurgy & Environment, Central South University, Changsha 410083, China;2. Engineering Research Center of the Ministry of Education for Advanced Battery Materials, Central South University, Changsha 410083, China;1. Department of Plastic and Aesthetic Surgery, Nanfang Hospital, Southern Medical University, Guangzhou, China;2. Department of Dermatology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA;3. Department of Oncology, Nanfang Hospital, Southern Medical University, Guangzhou, China;4. Department of Cell Biology, Johns Hopkins University, Baltimore, Maryland, USA;5. Department of Oncology, Johns Hopkins University, Baltimore, Maryland, USA;1. Department of Pathology and Center for Cancer Research, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA;2. Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA;3. Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA;4. Division of Hematology, Brigham and Women''s Hospital, Boston, MA 02115, USA;5. Department of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, MA 02215;6. SeqLL Inc., Woburn, MA 01801, USA;7. Department of Biological Regulation, Weizmann Institute of Science, Rehovot, Israel;1. Dipartimento di Scienze e Metodi dell’Ingegneria, via Amendola 2, 42122 Reggio Emilia, Italy;2. Centro Interdipartimentale En&Tech, Piazzale Europa, 1, 42124 Reggio Emilia, Italy;3. Dipartimento di Ingegneria Enzo Ferrari, via Vivarelli 10, 41125 Modena, Italy;4. National Interuniversity Consortium of Materials Science and Technology (INSTM), via Giusti, 50121 Florence, Italy;1. Departments of Genetics and Ophthalmology, Blavatnik Institute, Harvard Medical School, Boston, MA 02115, USA;2. Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA |
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| Abstract: | In the present work, polysomal structures, estimated to contain from two to seven 60 s monomers3, have been identified in HeLa cell mitochondria and some of their properties have been investigated. The study of mitochondrial polysomes has been facilitated by the use of RNase inhibitors, which reduced the contamination of these polysomes by endoplasmic reticulum-bound polysomes, and by the use of appropriate antibiotics, which allowed the selective labeling of either the nascent chains or the RNA components of the mitochondrial structures.Mitochondrial polysomes have revealed an unusual resistance to degradation by RNase; furthermore, only a partial dissociation of ribosomes into subunits and very little release of nascent chains were observed in the presence of even high concentrations of EDTA. The evidence derived from enzymic tests and from the comparison with the effects of RNase and EDTA on endoplasmic reticulum-bound polysomes, has suggested that this unusual behavior of mitochondrial polysomes is due to the nature of their polypeptide products, which makes the nascent chains particularly “sticky.” These chains would thus, on one hand, interact by secondary bonds with the two ribosomal subunits, stabilizing the ribosomes against dissociation by removal of Mg2+; on the other, they would interact with other chains on the same polysome, thus stabilizing the whole structure against degradation by RNase.The analysis of the distribution of mitochondrial rRNA among different ribosome structures has indicated that, under the present conditions of cell growth and of subcellular fractionation, about 50% of mitochondrial ribosomes are recovered in polysomes, about 20% as monomers and the rest as free subunits. |
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