[Degradation of 18S and 28S ribosomal RNA in the cytoplasm of rat liver cells after inhibition of protein synthesis].

Inhibition of protein synthesis (up to 95%) in starved rat liver cells after a single injection of a sublethal dose of cycloheximide (0.3 mg per 100 g of body weight) results in degradation of 18S rRNA during the first 3 hours, whereas the 28S rRNA remains unaffected. However, the increase of 28S rRNA degradation products was observed by the 6th and 12th hours. The rapid decay of 18S rRNA is due to the degradation of this RNA in 40S ribosomal subunits. In contrast to 28S rRNA the specific radioactivity of 18S rRNA is increased by the 6th hour. Presumably the synthesis and processing of 18S rRNA impaired during the 1st hour are recovered partially or completely by this time. A molecular mechanism underlying 18S rRNA degradation in 40S ribosomal subunits is proposed.