Cooper H L, Braverman R
J Cell Physiol. 1977 Nov;93(2):213-25. doi: 10.1002/jcp.1040930207.
During the initial ten hours of growth in lymphocytes stimulated by phytohemagglutinin, the cells are converted from a state in which over 70% of all ribosomes are inactive free ribosomes, to one in which over 80% of ribosomes are in polysomes or in native ribosomal subunits. In this initial period, there was a neglible increase in total ribosomal RNA due to increased RNA synthesis, and abolition of ribosomal RNA synthesis with low concentrations of actinomycin D did not interfere with polysome formation. Therefore, the conversion is accomplished by the activation of existing free ribosomes rather than by accumulation of newly synthesized particles. The large free ribosome pool of resting lymphocytes is thus an essential source of components for accelerated protein synthesis early in lymphocyte activation, before increased synthesis can provide a sufficient number of new ribosomes. Free ribosomes accumulate once more after 24 to 48 hours of growth, when RNA and DNA synthetic activity are maximal. This reaccumulation of inactive ribosomes at the peak of growth activity may represent preparation for a return to the resting state where cells are again susceptible to stimulation. Activation of free ribosomes to form polysomes appears to involve modification of at least two steps: (a) dissociation of free ribosomes with stabilization as native subunits, and (b) adjustment of a rate-limiting step at initiation.
在由植物血凝素刺激的淋巴细胞生长的最初十个小时内，细胞从一种状态转变为另一种状态，在初始状态下，超过70%的核糖体是无活性的游离核糖体，而在转变后的状态下，超过80%的核糖体存在于多核糖体或天然核糖体亚基中。在这个初始阶段，由于RNA合成增加，核糖体RNA总量的增加可以忽略不计，并且用低浓度放线菌素D消除核糖体RNA合成并不干扰多核糖体的形成。因此，这种转变是通过激活现有的游离核糖体来实现的，而不是通过新合成颗粒的积累。因此，静止淋巴细胞中大量的游离核糖体库是淋巴细胞激活早期加速蛋白质合成所需成分的重要来源，此时增加的合成还不能提供足够数量的新核糖体。在生长24至48小时后，当RNA和DNA合成活性达到最大时，游离核糖体再次积累。在生长活性高峰期无活性核糖体的这种重新积累可能代表着为恢复到静止状态做准备，在静止状态下细胞再次易于受到刺激。游离核糖体激活形成多核糖体似乎至少涉及两个步骤的修饰：(a)游离核糖体解离并稳定为天然亚基，以及(b)起始时限速步骤的调整。
