Zahradka P, Larson D E, Sells B H
Department of Molecular Biology and Genetics, College of Biological Science, University of Guelph, Ontario, Canada.
Eur J Biochem. 1989 Sep 1;184(1):261-6. doi: 10.1111/j.1432-1033.1989.tb15016.x.
Terminal differentiation of proliferating rat L6 myoblasts to syncytial multi-nucleated myotubes results in a decline in the cellular levels of 5S rRNA. This decrease parallels the drop in ribosome number and the reduction in 45S rRNA precursor gene transcription previously documented [Jacobs et al. (1985) Eur. J. Biochem. 150, 255]. The activity of RNA polymerase III in 100,000 x g supernatants from myoblasts and myotubes is similar suggesting the level of this enzyme does not limit 5S rRNA synthesis. Nuclear and cell-free transcription assays were used to measure 5S rRNA synthesis in myoblasts and myotubes. No differences were observed in the rate of 5S rRNA gene transcription, thus demonstrating that 5S rRNA levels in myotubes are not transcriptionally controlled. To determine whether RNA stability plays a role, the half-life of newly synthesized 5S rRNA was measured in vivo. The half-life of nuclear 5S rRNA was calculated to be 370 min and 65 min in myoblasts and myotubes, respectively, demonstrating that the decrease in 5S rRNA levels following terminal differentiation is regulated post-transcriptionally.
增殖的大鼠L6成肌细胞向多核肌管的终末分化导致5S rRNA细胞水平下降。这种下降与核糖体数量的减少以及先前记录的45S rRNA前体基因转录的减少平行[雅各布斯等人（1985年），《欧洲生物化学杂志》150卷，255页]。成肌细胞和肌管100,000×g上清液中RNA聚合酶III的活性相似，表明该酶的水平不限制5S rRNA的合成。使用核转录和无细胞转录试验来测量成肌细胞和肌管中5S rRNA的合成。未观察到5S rRNA基因转录速率的差异，因此表明肌管中5S rRNA水平不受转录控制。为了确定RNA稳定性是否起作用，在体内测量了新合成的5S rRNA的半衰期。核5S rRNA的半衰期在成肌细胞和肌管中分别计算为370分钟和65分钟，表明终末分化后5S rRNA水平的降低是在转录后调节的。
