Srivastava A K, Schlessinger D
Department of Microbiology and Immunology, Washington University School of Medicine, Saint Louis, MO 63110.
Proc Natl Acad Sci U S A. 1988 Oct;85(19):7144-8. doi: 10.1073/pnas.85.19.7144.
In Escherichia coli, the final maturation of rRNA occurs in precursor particles, and recent experiments have suggested that ongoing protein synthesis may somehow be required for maturation to occur. The protein synthesis requirement for the formation of the 5' terminus of 23S rRNA has been clarified in vitro by varying the substrate of the reaction. In cell extracts, pre-23S rRNA in free ribosomes was not matured, but that in polysomes was efficiently processed. The reaction occurred in polysomes without the need for an energy source or other additives required for protein synthesis. Furthermore, when polysomes were dissociated into ribosomal subunits, they were no longer substrates for maturation; but the ribosomes became substrates again when they once more were incubated in the conditions for protein synthesis. All of these results are consistent with the notion that protein synthesis serves to form a polysomal complex that is the true substrate for maturation. Ribosomes in polysomes, possibly in the form of 70S initiation complexes, may more easily adopt a conformation that facilitates maturation cleavage. As a result, the rates of ribosome formation and protein synthesis could be coregulated.
在大肠杆菌中，rRNA的最终成熟发生在前体颗粒中，最近的实验表明，正在进行的蛋白质合成可能以某种方式是成熟发生所必需的。通过改变反应底物，已在体外阐明了23S rRNA 5'末端形成对蛋白质合成的需求。在细胞提取物中，游离核糖体中的前体23S rRNA未成熟，但多核糖体中的前体23S rRNA得到了有效加工。该反应在多核糖体中发生，无需蛋白质合成所需的能量来源或其他添加剂。此外，当多核糖体解离为核糖体亚基时，它们不再是成熟的底物；但当核糖体再次在蛋白质合成条件下孵育时，它们又成为了底物。所有这些结果都与蛋白质合成用于形成作为成熟真正底物的多核糖体复合物这一观点一致。多核糖体中的核糖体，可能以70S起始复合物的形式，可能更容易采用促进成熟切割的构象。因此，核糖体形成速率和蛋白质合成速率可能受到共同调节。
