Transcription, the initial step of gene expression is a tightly regulated process. In addition to variability in the core promoter region of the RNA polymerase II transcribed genes, which can stabilize or destabilize the basal machinery and influence transcription rates, promoters contain enhancer regions which can be far upstream from the gene transcribed. These enhancers and their DNA binding factors are highly variable and can lead to the recruitment of unique co-activator complexes that can influence the initiation and progression of the polymerase through the nucleosomal structure of chromatin. In essence then, every promoter becomes a unique microenvironment, the sum of several enhancer elements, core promoter elements and chromatin structure. The gene’s transcription rate is then dependent on the efficiency of these interactions – an average of the effects of each enhancer and co-activator leading to a fine tuning of transcriptional responses according to cellular needs. It is therefore not surprising that transcription is the major checkpoint for gene expression in the cell. The next step for the new mRNA molecule is post-transcriptional modification, which augments the stability of the messenger mRNA export to the cytoplasm (in eukaryotes) and translation into proteins.
