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

The effect of the inclusion of EDTA and of heparin, in media used
in the isolation of mitochondria, on the mitochindrial previous
termribosomenext term has been investigated. 1. 1. Mitochondria
isolated from previous termNeurospora crassanext term in the
presence of EDTA contain only a single type of monomeric previous
termribosome, viz. 73next term S. 2. 2. Mitochondria isolated in
the presence of Mg2+ contain both 79-S and previous term73next
term-S monomeric previous termribosomes.next term The heterogeneity
of the previous termribosomesnext term was demonstrated by (a)
ultracentrifugation on sucrose gradients, (b) electron microscopy,
(c) immunoprecipitation with antibodies against mitochondrial
previous term73next term-S and 79-S cytoplasmic previous
termribosomes,next term (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 previous termribosomesnext
term resulted in (a) dissociation of previous term73next term-S
mitochondrial previous termribosomesnext term into 50-S and 37-S
subunits; (b) stabilization of 79-S cytoplasmic previous
termribosomes;next term (c) in the case of mitochondria isolated in
the presence of Mg2+ containing both previous term73next term-S and
79-S previous termribosomes,next term heparin causes the selective
dissociation of the previous term73next term S monosome to yield
previous termribosomesnext term containing only a single monomeric
previous termribosomenext term type, viz. 79 S. 4. 4. It is
concluded that (a) the 79-S previous termribosomesnext term present
in mitochondria isolated in the presence of Mg2+ are contaminating
cytoplasmic previous termribosomes,next term (b) the previous
term73next term-S previous termribosomesnext term are the real
functional mitochondrial previous termribosomes of Neurospora
crassanext term.