Dabeva M D, Dudov K P
Biochem J. 1982 Oct 15;208(1):101-8. doi: 10.1042/bj2080101.
Kinetic experiments of labelling in vivo with [14C]orotate of cellular free UMP and/or UTP, nucleolar, nucleoplasmic and cytoplasmic rRNA in normal and 12 h-regenerating rat liver were performed. The specific-radioactivity curves obtained were analysed by computer and the rates of synthesis of precursor rRNA (45S pre-rRNA) and cytoplasmic 28S and 18S rRNA calculated. (a) The rates of synthesis of 45S pre-rRNA in normal and regenerating rat liver are 1400 and 3700 molecules/min per nucleus respectively; (b) the average rates of formation of mature 28S and 18S rRNA are identical with the rates of synthesis of 45S pre-rRNA in both normal and regenerating rat liver. Thus the synthesis of rRNA in 12h-regenerating rat liver is activated 2.7-fold. The analysis of rRNA synthesis in isolated nucleoli also shows a 2.7-fold stimulation of transcription in regenerating liver. It is concluded that all the 45S pre-rRNA molecules synthesized are processed and transferred as 28S and 18S rRNA in the cytoplasm, i.e. degradation (wastage) of newly synthesized ribosomes in the nucleus does not occur in both normal and regenerating rat liver. Thus the enhanced production of ribosomes in regenerating rat liver is regulated only at the transcriptional level.
对正常和再生12小时的大鼠肝脏进行了体内用[14C]乳清酸标记细胞游离UMP和/或UTP、核仁、核质和细胞质rRNA的动力学实验。通过计算机分析得到的比放射性曲线，并计算前体rRNA（45S前体rRNA）以及细胞质28S和18S rRNA的合成速率。（a）正常和再生大鼠肝脏中45S前体rRNA的合成速率分别为每个细胞核每分钟1400和3700个分子；（b）成熟28S和18S rRNA的平均形成速率与正常和再生大鼠肝脏中45S前体rRNA的合成速率相同。因此，再生12小时的大鼠肝脏中rRNA的合成被激活了2.7倍。对分离的核仁中rRNA合成的分析也显示再生肝脏中转录受到2.7倍的刺激。得出的结论是，所有合成的45S前体rRNA分子都在细胞质中被加工并转化为28S和18S rRNA，即在正常和再生大鼠肝脏中，细胞核中新合成的核糖体不会发生降解（浪费）。因此，再生大鼠肝脏中核糖体产量的增加仅在转录水平受到调节。
