Ovalbumin Messenger Ribonucleic Acid Translation

Abstract Optimum conditions for translating ovalbumin messenger RNA in a cell-free, protein-synthesizing system derived from rabbit reticulocytes were similar to those for endogenous globin messenger RNA. At suboptimal conditions the translation of ovalbumin messenger RNA was usually inhibited more than globin messenger RNA. Hemin prolonged the synthesis of both proteins, and Q, an inhibitor of initiation formed during incubation, inhibited the translation of both messengers. The rates of elongation on ovalbumin and globin messenger RNA were nearly identical at 0.86 amino acid per s at 26°, and were maintained for at least an hour. After 10 min of incubation, ovalbumin was synthesized on polysomes composed of 9 ribosomes (75% of the maximum size possible), corresponding to a rate of initiation of about 1.1 ribosomes per min at 26°. The size of ovalbumin-synthesizing polysomes gradually fell to 3 during a 70-min incubation. The rate of initiation on globin messenger RNA was about 30% faster than on ovalbumin messenger RNA, but there was a corresponding decrease in this rate during incubation. Ovalbumin messenger RNA was not degraded in the proteinsynthesizing system. These results suggest that protein synthesis stops in this system due to a failure of polypeptide initiation. The efficiency of messenger RNA translation was estimated by two independent methods. Both methods indicate that each globin messenger RNA was translated about 70 times during a 90-min incubation. Each ovalbumin messenger RNA was translated about 45 times according to one method, but only up to 18 times by the other. The ratio of the values obtained by these two methods is a means of estimating the percentage of active messenger in an RNA preparation.