The 73 S ribosome of Neurospora crassa is the native mitochondrial ribosome

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Abstract

The effect of the inclusion of EDTA and of heparin, in media used in the isolation of mitochondria, on the mitochindrial ribosome has been investigated.

  • 1.

    1. Mitochondria isolated from Neurospora crassa in the presence of EDTA contain only a single type of monomeric ribosome, viz. 73 S.

  • 2.

    2. Mitochondria isolated in the presence of Mg2+ contain both 79-S and 73-S monomeric ribosomes. The heterogeneity of the ribosomes was demonstrated by (a) ultracentrifugation on sucrose gradients, (b) electron microscopy, (c) immunoprecipitation with antibodies against mitochondrial 73-S and 79-S cytoplasmic ribosomes, (d) gel electrophoresis of high and low molecular weight RNAs.

  • 3.

    3. Inclusion of heparin in all media used for the isolation of mitochondria and ribosomes resulted in (a) dissociation of 73-S mitochondrial ribosomes into 50-S and 37-S subunits; (b) stabilization of 79-S cytoplasmic ribosomes; (c) in the case of mitochondria isolated in the presence of Mg2+ containing both 73-S and 79-S ribosomes, heparin causes the selective dissociation of the 73 S monosome to yield ribosomes containing only a single monomeric ribosome type, viz. 79 S.

  • 4.

    4. It is concluded that (a) the 79-S ribosomes present in mitochondria isolated in the presence of Mg2+ are contaminating cytoplasmic ribosomes, (b) the 73-S ribosomes are the real functional mitochondrial ribosomes of Neurospora crassa.

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    Present address: Department of Botany, University College Dublin, Irish Republic.

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