1. Rat-liver microsomes, ribonucleoprotein particles and a fraction mainly consisting of microsomal membranes were tested for their ability to incorporate amino acids into protein in the presence of ATP, GTP, phosphoenolpyruvate and pyruvate kinase. Addition of polyuridylic acid or of ribonucleic acid from rat-liver nuclei stimulated the incorporating activities. 2. These protein-synthesizing s...

The nature and properties of the 20S ribonucleic acid which accumulates only during the sporulation of Saccharomyces cerevisiae were examined. The 20S ribonucleic acid (RNA) has a base composition considerably different from ribosomal RNA species and is virtually unmethylated. The 20S RNA did, however, exhibit approximately 70% homology with 18S RNA by RNA-deoxyribonucleic acid filter hybridiza...

Sporangiomycin and micrococcin inhibit the binding of aminoacyl-transfer ribonucleic acid into the ribosomal A site in intact bacterial protoplasts. They also prevent the assembly of [ribosome-elongation factor G-guanine nucleotide] complexes in vitro and compete with [(35)S]thiostrepton for ribosomal binding sites. We conclude that micrococcin and sporangiomycin block the ribosomal A site in t...

Thermal denaturation of plant ribosomal RNA followed by gel fractionation shows that although a large percentage of molecules contain breaks in the polynucleotide chain, 25S and 18S RNAs do exist as unique molecular species. Values for the rate constant of hydrolysis under routine denaturing conditions are of the order of 10(-7) to 10(-8) sec(- 1) and these are shown not to be a result of ribon...