Physiology of rat-liver polysomes. The stability of messenger ribonucleic acid and ribosomes.

Starvation of rats for several days led to marked decrease in cytoplasmic polysomes and accumulation of breakdown products having S values less than 200s. Re-feeding of the starved animals induced a rapid reassembly of polysomes. These newly formed polysomes, in the presence of actinomycin D, decayed in a biphasic fashion: about two-thirds decayed with an apparent half-life of 3-3(1/2)hr. but the other one-third were much more stable. Evidence that polysome decay is an accurate reflexion of messenger RNA stability is presented, and it is concluded that in the presence of large doses of actinomycin D, rat-liver cytoplasm contains messenger RNA classes of widely varying stability, the more stable class having a half-life of at least 80hr. The half-life of liver ribosomes was also determined and was found to be 110-127hr.