The aim of this short review is to comment on the advantages of injecting purified molecules into a normal living cell as a complement to the constitution of a cell-free system for analyzing the function of cell components. We emphasize here that the major difference is that, by injection, most components of a cell are maintained at their normal concentration, which is difficult, even if at all possible, to achieve in a cell-free system. We exemplify the benefits of a cell injection system by the efficiency and long duration of DNA transcription by RNA polymerase II, as used by most genes, and by the widespread success of injecting purified messenger RNA for protein synthesis. The most recent work using cell injection also gives a new understanding of a long lasting transcription factor residence on its DNA or chromatin not shown by other procedures. Lastly, we re-visit an old idea that transcription factors that guide cell fate may be stably bound to DNA or chromatin, except at S-phase or mitosis in the cell cycle, when they can undergo exchange with equivalent molecules in the cell.

这篇简短评论的目的是评论将纯化的分子注射到正常的活细胞中作为对用于分析细胞成分功能的无细胞系统构成的补充的优势。在这里我们强调主要的区别在于，通过注射，细胞的大多数成分都保持在其正常浓度，即使在完全可能的情况下，也很难在无细胞系统中实现。我们通过大多数基因使用的RNA聚合酶II进行DNA转录的效率高和持续时间长，以及通过注射纯化的信使RNA进行蛋白质合成的广泛成功，来例证细胞注射系统的优势。使用细胞注射的最新工作还对转录因子在其DNA或染色质上的持久滞留有了新的认识，而其他方法未对此进行展示。最后，我们重新考虑一个古老的想法，即引导细胞命运的转录因子可以稳定地与DNA或染色质结合，但在S周期或细胞周期中的有丝分裂时，它们可以与细胞中的等效分子进行交换。