The production of RNA (mRNA, rRNA, miRNA, etc.) occurs through a process known as transcription. This process occurs in a well-defined sequence, starting with the selection of one or two sites on the DNA that encode for the appropriate RNA. A polymerase complex will then assemble, and begin translocating along the DNA, producing the RNA as it moves. Finally, the RNA must be processed and transported out of the nucleus and processing is different for mRNA versus the other types. In differentiated mammalian cells, transcription initiation sites are partially determined by the silencing of major portions of the chromatin through post-translational modifications. In addition, there are tissue-specific aspects of mRNA production that include alternative splicing of the mRNA, and micro-RNAs, which decrease the lifetime of mRNA subsets. There has been considerable interest in how the cell transcribes the right DNA, processes and then packages the transcript for transport to the cytoplasm. To fully understand the primary signals that govern gene expression, the expression levels of various transcription factors must be defined, and more comprehensive data on the changes in transcription patterns attained. For sufficient specificity, and regulation of the transcription process, we would expect several factors to interact with the DNA or transcription machinery. Thus, the definition of the site of transcription is the critical aspect and the subsequent process of mRNA production and processing follows as expected.

Steps in mRNA production and processing:

To introduce the topic of RNA production and processing, we will first consider how proteins are produced in cells. Cells transcribe DNA into RNA as a first step towards producing functional protein complexes. Once again, the principles of manufacturing a car are analogous in many ways to this important cellular process. In a well-run automobile factory, each car is produced from a set number of parts, each of which is incorporated in a set sequence. Highly specialized machines are required to both produce the parts and incorporate them into the final product. It would be wasteful to produce an excess of any one part, and incorporating a part out of sequence will render the car unusable, and slow down further production.