The process by which a short strand of RNA (m-RNA) is formed on the template of DNA in the nucleus (eukaryotes) or in the cytoplasm is known as transcription. It requires various enzymes, particularly RNA polymerase which is a holoenzymes, i.e., made up of a protein part called core enzyme and a non-proteinacious called ct (sigma) factor. Core enzyme, individualy can take part in transcription but it does not initiate transcription at proper site in the absence of o factor.