Specific molecules found in one cell have a regulatory function, those regulatory molecules can be activator proteins that bind to the regulatory sites of the DNA acting as a on/off switches in the process of transcription, since the RNA that will be formed can be translated into different amino acid sequences. The CRISPR-Cas9 system is a example of gene expression supressor and activator used in molecular biology as a gene edit tool. The process of gene activation start when a transcription factor (protein) bind to bits of the DNA (that are marked by a promoter), the sequence marked is transcribed into a molecule of mRNA, this RNA will be translated in the cytoplasm into a animo acid sequence that will form a protein, being that protein from the gene "selected" and "marked" by the transcription factors. Each cells have they transcription factors, and the moment that they are triggered to work by an intracellular or extracellular stimulus.
