ACTIVATION IN VITRO OF RAT LIVER POLYRIBOSOMES

The increase in the incorporation of amino acids into protein in vitro by preparations obtained from protein-fed rats as compared with preparations obtained from carbohydrate-fed rats has been described previously. After molecular sieving through Sephadex G-25 of cell-free preparations, the difference in incorporating activity between the two types of rats was diminished in systems containing ATP, phosphoenolpyruvate, pyruvate kinase, GTP, and a mixture of amino acids. When, after molecular sieving, a mitochondrial (15,000 g) supernatant was incubated for 4 min at 35°C the polysomal pattern of the preparations was unchanged. In the presence of ATP, phosphoenolpyruvate, and pyruvate kinase the polysomal incorporating activity was low and the polysomal pattern was only slightly changed. Addition of GTP increased the activity markedly, and a more pronounced activity was observed when a mixture of amino acids was added as well. As the amino acid incorporation ability increased, monosomes were formed from the polyribosomes. The activity of the polyribosomes was severalfold higher than that of non-Sephadex-treated preparations, indicating an activation of polysomal aggregates which under the usually applied conditions of incubation and prior to molecular sieving show little or insignificant activity. It was possible to activate polyribosomes from carbohydrate-fed and protein-fed rats to almost the same extent.     

The Use of Nucleoside Phosphotransferase and (P) p-Nitrophenyl Phosphate in the Determination of the 5'-Linked Termini of Ribosomal RNA

A method for the identification of the 5′-linked termini of ribosomal RNA is described. The method involves the phosphorylation of the nucleosides released from the 5′-linked termini after hydrolysis of the ribonucleic acid chain with alkali. The radioactive 5′-nucleotide derivatives are formed by a nucleoside phosphotransferase mediated phosphoryl transfer from (³²P) p-nitrophenyl phosphate to the nucleosides. The sensitivity of the method allows the use of small amounts of ribosomal RNA.     

Effect of Different Nitrogen Sources on the Cellular Form of Trigonopsis variabilis

Triangular cells are formed during early logarithmic growth of Trigonopsis variabilis. Good triangularity is obtained with methionine, proline, hydroxyproline, or alanine as a nitrogen source.     

Nuclear track registration in solids by etching

Summary A review is given on recent developments in the field of charged particle track registration in insulating solids by preferential etching. The basic mechanism of latent track formation in minerals and inorganic glasses seems to be a spike formation process. In the more sensitive organic polymers, radiation induced chemical changes along the track probably predominate. The sensitivity, etching kinetics, and stability of tracks in plastics and some of the factors which affect them are discussed on the basis of experimental data.Several microscopic and macroscopic methods for simplified or automatic track counting are described briefly. Among the many applications of the etching method, neutron dosimetry via (n, f), (n, ), and recoil reactions are discussed in some detail. Other applications in nuclear physics, chemistry, biology, space research, and for age determinations in geological and archeological samples are listed.Research sponsored by the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation.Based on a lecture at the University of Tennessee, February 13, 1968.