Inhibition of friend murine leukemia virus production by low-ionic-strength medium.

The effect of medium of low ionic strength on the release of virus from Friend leukemia cells has been studied. The release of infectious Friend leukemia virus is almost completely inhibited in medium of low ionic strength, as measured by a focus-forming assay (XC assay), by endogenous RNA-dependent DNA polymerase activity of released virus particles, and by electron microscope studies of the production of C-type particles. Friend leukemia virus-transformed proerythroblasts undergo extensive morphological changes in low-ionic-strength medium. The cells are viable in this medium, but they can no longer be stimulated with dimethyl sulfoxide to produce hemoglobin and increase virus production. Infectious virus is released between 30 and 120 min of resuspension of inhibited cells in normal medium. The rate of virus release after reversal of the inhibition is much greater than the rate of virus release during normal cell growth. The morphological changes occurring after dimethyl sulfoxide stimulation of Friend leukemia cells are compared with those resulting from resuspension in normal medium of cells inhibited by low ionic strength.

Globin mRNA translation on Artemia salina ribosomes with components from Friend leukemia cells.

Globin mRNA can be translated with relatively high efficiency in a fractionated cell-free system containing ribosomes prepared from cytst of Artemia salina. These ribosomes have unusually low endogenous activity for peptide synthesis in the absence of added mRNA. The system requires components from the postribosomal supernatant and from the 0.5 M KCl ribosomal wash fraction. Both these fractions were derived from either rabbit reticulocytes or unstimulated Friend leukemia cells that produce little or no hemoglobin. The activity of mRNA and enzyme fractions from rabbit reticulocytes and Friend leukemia cells were tested in this system in vitro for their ability to direct the synthesis of the alpha and beta chains of globin. The alpha:beta chain ratio synthesized from mRNA in the rabbit reticulocyte salt wash fraction was 4:1. The corresponding value for the 9-S mRNA fraction from the salt-washed reticulocyte ribosomes was 1:4, thus these two fractions appear to provide sources enriched in either alpha or beta globin mRNA. Under all conditions tested, the ratio and amounts of peptides formed in vitro appear to reflect mRNA composition. Globin mRNA from dimethysulfoxide-stimulated Friend leukemia cells when translated in vitro produced alpha and beta chains in a ratio of 1:1. These peptides are formed in the same ratio in the intact cells.