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Translation of the polysomal mRNA of mouse myeloma cells in a wheat germ cell-free system leads to the immunoglobulin (Ig) light-chain precursor as the major product. Excess polysomal RNA causes strong inhibition of polypeptide synthesis, but has little effect of light-chain precursor synthesis. The inhibitory effect of excess RNA is avoided when the poly(A)-containing RNA fraction is used. With nearly saturating amounts of the latter RNA, light-chain recursor synthesis becomes more predominant, possibly as a result of competition between different mRNA species. High levels of potassium acetate cause strong inhibition of overall translation, but do not inhibit light-chain precursor synthesis. Addition of poly(A) to the cell-free system also causes inhibition, presumably through interference with the intiation process. Again, light-chain precursor synthesis is relatively resistant. Ig heavy-chain synthesis is relatively inefficent, but its resistance to the inhibitors tends to be nearly as great as that of the light-chain precursor. The results indicate that the Ig mRNAs are particulary efficient in initiating translation. This characteristic may account for certain features of the regulation of Ig synthesis in intact myeloma cells.
Sonenshein et al. (Wed,) studied this question.