The 32 S RNA of Neurospora crassa mitochondria is not a precursor of the mitochondrial ribosomal RNAs.

Studies on the synthesis of Neurospora mitochondrial ribosomal RNAs by Kuriyama &; Luck 1973 have led to the currently accepted idea that the mature 19 S and 25 S rRNA species are synthesized via a common 32 S precursor RNA. The present results provide evidence that the 32 S RNA band analyzed by Kuriyama &; Luck was in fact a mixture of low concentrations of rapidly labeled RNA species, probably including separate precursors of 19 S and 25 S RNA, along with higher concentrations of aggregates of mature 19 S and 25 S RNA. The former account for the pulse-labeling characteristics of the 32 S band, whereas the latter contribute most of the mass-label, resulting in misleading hybridization data.