The Decay of Xenopus laevis Mitochondrial rRNA in the Presence of Ethidium Bromide or Actinomycin D

The effect of ethidium bromide and actinomycin D on prelabelled mitochondrial RNA was studied in Xenopus laevis embryos. Mitochondrial rRNA was found to decay with a half-life of 2–2.5 h following an initial lag of < 2 h. There was an initial increase in incorporation into mitochondrial rRNA in the presence of actinomycin D but not in the presence of ethidium bromide. Radioactivity in mitochondrial 4 S RNA rises and then is relatively stable for the duration of the chase period. Cytoplasmic rRNA and 4 S RNA are stable under the chase conditions used, and, in the presence of ethidium bromide, cytoplasmic RNA continues to be synthesized.