Translation in vivo and in vitro of mRNAs Coding for Vitellogenin, Serum Albumin and Very-Low-Density Lipoprotein II from Chicken Liver. A Difference in Translational Efficiency

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Abstract
Characterization of polysomes from estrogenized chicken liver revealed that very low density lipoprotein II (VLDLII), serum albumin and vitellogenin mRNA are differently packed with ribosomes during translation in vivo. The ribosome density per number of nucleotides is high for VLDLII mRNA, intermediate for serum albumin mRNA and low for vitellogenin mRNA. This difference in ribosomal load is maintained throughout the period of hormone effect. The differential use observed for vitellogenin and VLDLII mRNA partly explains the large difference in molar production rate between these yolk protein precursors. Translation properties and efficiency of the 3 hepatic mRNA were also compared in the mRNA-depleted reticulocyte lysate. Elongation of the nascent chains for vitellogenin and serum albumin proceeded in a discontinuous fashion. Initiation in vitro was studied at varying ionic strengths, in the presence of aurintricarboxylic acid and at suboptimal hemin concentrations. VLDLII mRNA expression is by far the most resistant to 7-methyl-GTP and high salt concentrations, vitellogenin mRNA the least. This behavior resembles the differential use of the mRNAs in vivo. The putative structural basis of these differences is discussed.