Agrawal M G, Bowman L H
J Biol Chem. 1987 Apr 5;262(10):4868-75.
The metabolism of ribosomal proteins (r-proteins) and r-protein mRNAs was examined during mouse myoblast differentiation to identify the levels at which r-protein accumulation is regulated. Pulse-chase analyses of r-proteins in myoblasts and fibers indicate that the synthesis of r-proteins is coordinately reduced 2.0-fold following myoblast differentiation and that newly synthesized r-proteins do not turnover. This decreased synthesis of r-proteins in fibers is due to both a reduction in the steady-state levels of r-protein mRNAs and a decrease in the translational efficiency of r-protein mRNAs. Northern analyses of r-protein mRNA indicate that the steady-state levels of r-protein mRNAs S16, L18, and L32 are decreased 1.5-2.0-fold in fibers as compared to myoblasts. Analyses of the distribution of r-protein mRNAs in polysome gradients indicate that their translational efficiencies are reduced 1.3-1.6-fold in fibers as compared to myoblasts. To determine if the decrease in the steady-state levels of r-protein mRNAs is regulated at the level of transcription, the transcription of these genes was measured in isolated nuclei. These experiments show that the transcription of these r-protein genes is reduced 2-6-fold following myoblast differentiation. Thus, the production of r-proteins is regulated both at the level of transcription and translation during mouse myoblast differentiation.
在小鼠成肌细胞分化过程中，对核糖体蛋白（r蛋白）和r蛋白mRNA的代谢进行了研究，以确定r蛋白积累的调控水平。对成肌细胞和肌纤维中r蛋白的脉冲追踪分析表明，成肌细胞分化后，r蛋白的合成协同降低了2.0倍，并且新合成的r蛋白不会周转。肌纤维中r蛋白合成的减少是由于r蛋白mRNA的稳态水平降低以及r蛋白mRNA的翻译效率降低。对r蛋白mRNA的Northern分析表明，与成肌细胞相比，肌纤维中r蛋白mRNA S16、L18和L32的稳态水平降低了1.5 - 2.0倍。对多核糖体梯度中r蛋白mRNA分布的分析表明，与成肌细胞相比，其在肌纤维中的翻译效率降低了1.3 - 1.6倍。为了确定r蛋白mRNA稳态水平的降低是否在转录水平受到调控，在分离的细胞核中测量了这些基因的转录。这些实验表明，成肌细胞分化后，这些r蛋白基因的转录降低了2 - 6倍。因此，在小鼠成肌细胞分化过程中，r蛋白的产生在转录和翻译水平均受到调控。
