Translation of Duck-Globin Messenger RNA in a Partially Purified Mammalian Cell-Free System

Duck globin messenger RNA purified by three different procedures from duck immature erythrocyte polyribosomes was translated in a mammalian cell-free system which is strongly dependent upon exogenous mRNA. The system consists of purified mouse liver ribosome sub-units, partially purified rabbit reticulocyte initiation factors, and rat liver pH-5 enzymes (containing elongation and termination factors, aminoacyl-tRNA synthetases and tRNA). If offered alone, duck globin mRNA directed the synthesis of all known duck globin chains. The efficiency of duck globin synthesis was similar to that of rabbit globin if the two types were translated separately. If duck and rabbit globin mRNA were offered together each in saturating amounts in this system, rabbit globin synthesis occurred almost exclusively. Differences in the secondary structure between the two types of globin mRNA must be involved in this strongly discriminating translation in the competition experiments. Furthermore, the quantitative requirement of at least one initiation factor was found to be different for duck and rabbit globin mRNA translation. While there is no evidence that this factor is directly involved in mRNA binding, it seems likely that the difference in factor requirement is related to the preferential translation of rabbit globin mRNA in the competition experiments.