Translational Competition by mRNA Species Encoding Albumin, Ferritin, Haemopexin and Globin

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Abstract
MRNA from rat liver was translated in a micrococcal-nuclease-treated reticulocyte lysate supplemented with liver tRNA. Synthesis of the liver proteins hemopexin, ferritin and albumin was analyzed by quantitative immunoprecipitation. The relative translation yield of these proteins changed as a function of the amount of mRNA present during protein synthesis, revealing the existence of translational competition between individual species of mRNA from the liver. The mRNA species encoding hemopexin, ferritin and albumin possess distinctly different abilities to compete for one or more critical components in translation, with competitive strength increasing in this order. Although on a weight basis total liver mRNA is apparently as effective a template for protein synthesis as is globin mRNA, the latter displays a greater resistance to inhibition of its translation by KCl. In analogy with the translation properties of .alpha.-globin and .beta.-globin mRNA globin mRNA may possess greater competitive strength than does total liver mRNA. Increasing amounts of globin mRNA competitively inhibit the translation of albumin and ferritin mRNA present in total liver mRNA. The competition is relieved by the addition of eukaryotic initiation factor eIF-2. Translation of ferritin mRNA responds more vigorously to relief by eIF-2 than does translation of albumin mRNA, a finding consistent with the observation that albumin mRNA competes more effectively than ferritin mRNA in translation. Albumin mRNA may possess a greater affinity for eIF-2 than does ferritin mRNA.