Cell genomes contain thousands of genes. However, the cell does not need all the proteins all the time. At any given moment only certain proteins are required. Therefore, cell needs to be able to regulate gene expression (to turn genes on and off).
What is the "least expensive" way for the cell to regulate gene expression?
ANTIBIOTICS, TRANSCRIPTION INHIBITORS
Initiation of transcription in prokaryotes and eukaryotes is substantially different. Some drugs affect specifically only prokaryotic transcription machinery. For example, antibiotic RIFAMPICIN is an inhibitor of prokaryotic transcription initiation. It binds only to bacterial RNA polymerase but not to eukaryotic RNA polymerases. Therefore, rifampicin is a powerful drug for treatment of bacterial infections.
