Translational Control of Antibody Synthesis.

Mouse plasma cytoma cells (5563) contain 2.5 times more L-chain mRNA than H-chain mRNA. The ratio of L- to H-chain produced however appears related to the growth rate of the cells. During exponential growth, up to 2.5 times more L-chain than H-chain protein is produced, but as cells approach stationary growth phase, L- and H-chain protein approach equal synthesis. The apparent decrease in L-chain synthesis upon shifting from exponential to stationary growth appears not to be due to a relative reduction in peptide elongation but rather reflects differences in ribosome loading. During exponential growth, L-chain polyribosomes contain 6–8 ribosomes/L-chain mRNA whereas in stationary growth, L-chain polyribosomes contain 3–4 ribosomes/L-chain mRNA. A similar shift of polyribosome size is noted with total cellular polyribosome. Polyribosomes engaged in H-chain synthesis remain fully loaded with ribosomes during conditions of L-chain polyribosome size reduction. The size of polyribosomes synthesizing H-chain protein can be reduced however under conditions of an increase in the intracellular level of H2L2. [ABSTRACT FROM AUTHOR]

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