Abstract
Two mammalian systems have been developed for efficient in vitro translation of exogenous messenger RNA (rabbit globin mRNA). One system is completely derived from guinea pig brain, and the other is from liver of different species. Both systems consist of purified 60S and 40S ribosomal sununits, unseparated initiation factors partially purified by ammonium sulfate precipitation and DEAE-cellulose chromatography, and pH 5 enzyme fractions as sources of elongation and termination factors, aminoacyl-tRNA synthetases, and transfer RNA. Translation depends completely upon exogenous mRNA and initiation factors. Extraction of initiation factors from microsomes or ribosomes has been improved for these tissues by inclusion of Mg(++) ions in the 0.5 M KCl extraction solution. Both systems synthesize complete rabbit alpha- and beta-globin chains, but in variable ratios. The overall efficiencies of the two systems are about 60% (liver) and 40% (brain) of a comparable system with rabbit reticulocyte initiation factors.