| Abstract: | The ability of embryonic chicken muscle initiation factors to translate rabbit globin messenger RNA in an efficient, fractionated cell-free system has been examined. Although muscle factors stimulate leucine incorporation to only 15--35% the levels achieved with rabbit reticulocyte initiation factors, they synthesize more than one globin chain per mRNA molecule and both alpha and beta globin are produced. Increasing the ribosome concentration and adding the polyamine spermidine to the system produce stimulatory effects which are quantitatively and qualitatively similar for both factor preparations. The lower efficiency of synthesis of muscle factors relative to reticulocyte factors is also apparent when mRNA from encephalomyocarditis virus or embryonic chicken muscle polysomes are used in the cell-free system. These results do not support a specific restriction in the capacity of muscle factors to translate globin mRNA. Furthermore, the similarity of the effects of presumed non-specific components on the activity of muscle and reticulocyte factors suggests that globin synthesis in the cell-free system may be controlled in a similar fashion for both preparations. |
