The expression of a gene is said to be ‘turned on’ when certain signals interact with the promoter of a gene and RNA is produced. The strand of RNA that corresponds to a gene is complementary to the sequence of DNA. The process called "Transcription" is:

the process of transcription is defined as a process by which cells are able to allow for expression of their genes. this involves how DNA is read and written into RNA (mainly messenger RNA). mRNA production then guides the synthesis of various proteins. the process of transcription occurs in three stages which include initiation, elongation and termination. when certain signals interact with the promoter of a gene, transcription is initiated allowing for some regions of the DNA to be transcribed in the 5 to 3' direction. such that the newly synthesized strand of mRNA is complementary to the non coding sequence. Controlling the production of mRNA in the nucleus allows the regulation of gene expression.