Increased transcription and decreased degradation control and recovery of liver ribosomes after a period of protein starvation.

In the livers of 5-days-protein-depleted mice there is a decrease of 47% of the ribosome mass. When these animals are fed with an adequate diet, ribosome content is restored to the normal value after 1 day of re-feeding. The mechanisms underlying this phenomenon were studied. It was found that: (1) the activity of RNA polymerase I in the nuclei of livers from re-fed animals showed an enhancement of about 2-fold compared with the activity in normal and protein-depleted liver nuclei; (2) ribosome degradation, measured by the disappearance of radioactivity from ribosomal proteins previously labelled by the administration of NaH14CO3 to the mice, stopped during the first day after re-feeding.