Leucine and phenylalanine incorporation by rat liver microsomes containing endogenous template RNA: a kinetic study of the effect of polyuridylic acid

Quantity and translation efficiency of liver microsomes in young and old rats following partial hepatectomy

1. Liver microsomal quantity decreased in young rats 2 days after partial hepatectomy or sham operation, increased to preoperative values by 8 days, and remained unchanged 16 days following surgery. 2. In old rats, microsomal quantity remained unchanged following surgery, but increased in sham-operated controls. 3. Translational efficiency of microsomes from young, sham-operated animals was unaffected, but decreased 2 days after partial hepatectomy. 4. In old, sham-operated controls, efficiency decreased, but remained unchanged 2 days after partial hepatectomy. 5. Eight and 16 days after surgery, efficiency of microsomes from young and old animals appeared indistinguishable, and were similar to those of adults before surgery.

Effect of biotin on ribonucleic acid synthesis

A single injection of biotin to biotin-deficient rats produces a two-fold increase in the incorporation, both in vivo and in vitro of precursors into nucleic acids as early as 2 h after the biotin treatment. The specific activity of the precursor pool is not affected by biotin. Analysis of the polysome profile at various times following biotin treatment and a kinetic study of the effect of excess poly(U) on the incorporation of phenylalanine by cell-free amino acid incorporation experiments indicate a marked decrease in messenger-free ribosomes in rat liver after biotin administration.

Initiation factor distribution in Xenopus laevis eggs

The distribution of activity similar to that of one of the initiation factors (IF2) was determined as a function of developmental stage in Xenopus laeviseggs and embryos. In vivo exposure of mature oocytes to hormone increases the total amount of detectable factor activity and facilitates the binding of IF2-like factor to ribosomes. The quality of factor bound is not correlated with polysome content.