Cytoplasmic-type 80 S ribosomes associated with yeast mitochondria. I. Evidence for ribosome binding sites on yeast mitochondria.
نویسندگان
چکیده
A class of 80 S ribosomes has been isolated from purified yeast mitochondria. These ribosomes are distinguished from cytoplasmic ribosomes of the postmitochondrial supernatant fraction by having a greater stability against the dissociating effect of 0.4 M KCI. These results confirm observations of Schmitt ((1969) Fed. Eur. Biochem. Sot. Left. 4, 234-238). Ribosome dissociability has been examined as a function of the stage of cell growth. Free and membranebound cytoplasmic ribosomes of the postmitochondrial supernatant fraction and the 80 S ribosomes associated w,ith mitochondria are all more resistant to the dissociating effect of 0.4 M KC1 when isolated from log phase as compared with stationary phase cells. In all cases, however, 80 S ribosomes associated with mitochondria show resistance to KC1 dissociation to a significantly larger degree than do the other classes of ribosomes. Three lines of evidence support the conclusion that the 80 S ribosomes (bound 80 S) we isolate from purified mitochondria are cytoplasmic-type ribosomes: (a) incorporation of 32Pi into rRNA of these 80 S ribosomes is insensitive to 15 pg per ml of ethidium bromide, (b) this class of 80 S ribosomes is found in the mitochondrial fraction from a cytoplasmic petite which lacks mtDNA, and, (c) poly(U)-directed phenylalanine incorporation catalyzed by purified preparations of 80 S ribosomes associated with mitochondria is sensitive to inhibition by cycloheximide but not by chloramphenicol. Evidence is presented that purified mitochondria have binding sites for the bound 80 S ribosomes; additional binding sites can be exposed by washing mitochondria with 2 mu EDTA. We observe at least two classes of binding sites with EDTA-washed mitochondria. “Low affinity” sites bind 260 pg of ribosomes per mg of mitochondrial protein and “high affinity” sites bind 116 pg of ribosomes per mg of mitochondrial protein. Ribosome binding sites on EDTA-washed mitochondria are labile; storage of mitochondria at 0” reduces their ability to bind exogenously added bound 80 S ribosomes in an apparent first order process with a half-life of 33 hours.
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ورودعنوان ژورنال:
- The Journal of biological chemistry
دوره 247 24 شماره
صفحات -
تاریخ انتشار 1972