ABSTRACT
All RNA is generated by transcription. The initiation of the process requires RNA polymerase to bind to the promoter region present in the DNA. Promoter regions are located 5′ of the region that will be transcribed into RNA. Transcriptional regulation modifies the frequency of transcription, regulating the amount of RNA made. For some RNAs, transcription occurs at a relatively consistent level. The coding regions encoded by these RNAs are said to have constitutive expression, which means that the genes are transcribed at roughly the same levels at all times. This does not mean that all constitutively expressed genes are expressed at the same levels relative to each other; the individual levels of expression vary depending on the gene. Constitutive expression refers only to the level of transcription of the gene being equal regardless of the state of the cell.
