The state of messenger ribonucleic acid and ribosomes in the cytoplasm of ethionine-treated rat liver.

The administration of ethionine to female rats causes breakdown of hepatic polysomes. The state of mRNA and monomeric ribosomes after the polysome dissociation was studied. The mRNA was selectively labeled with [14C] orotate after a low dose of actinomycin D. Sucrose density gradient centrifugation of Triton X-100-treated cytoplasm revealed an accumulation of heterodisperse radioactive material with very large S values. This material was converted to smaller S values with deoxycholate treatment and was extremely sensitive to mild ribonuclease treatment. Since this material was banded at around 1.43 g/cm3 in CsCl gradient centrifugation and contained RNA with a distribution of S values characteristic of polysomal mRNA, this material was identified as mRNA-containing ribonucleoprotein particles. The monomeric ribosomes were shown to be dissociated into subunits in the presence of 0.5 M KCl, indicating that these lacked nascent polypeptide chains. When the animals were recovered from the ethionine treatment by subsequent administration of adenine and methionine, the heterodisperse ribonucleoprotein particles and monomeric ribosomes appeared to be utilized for the reformation of polysomes.