RNA acts as an interim molecule that can amplify gene expression much better than directly translating the protein from the DNA. An interim template offers multiple levels of regulation that proceeding directly from DNA to the protein does not. By regulating the stability of the mRNA, the up-regulation of more copies of the protein is ensured. It also allows for greater flexibility when down-regulating gene expression; in other words, without mRNA it would be difficult to down-regulate gene expression. Translation would become incredibly complicated as it would have to both ensure correct translation and regulate the rate of initiation of translation. Repressors, activators, and enhancers would need to work on the ribosome. This would add another level of complexity to an already complex process of translation. Without mRNA, eukaryotic translation could not occur in the cytoplasm, nor could alternative splicing produce a wide variety of proteins from one gene.
