Promoters are the specific DNA sequences that are required for the expression of genes. These DNA sequences direct the RNA polymerase to bind to the specific regions of the gene. For example, the DNA sequences present at -10 and -35 regions of genes of E. coli interact with the sigma subunit of RNA polymerase and direct it where to bind during the process of transcription.
Eukaryotic genes do not have the prokaryotic promoters. Therefore, bacterial promoter sequences should be added to a eukaryotic gene to allow its expression in a prokaryotic cell.
