Formation of mRNA from DNA is called as transcription. It is heterocatalytic function of DNA, template of DNA called sense strand (master strand) is involved. The segment of DNA involved in transcriptions is cistron, which have a promoter region, where initiation starts and terminator region, where rranscription ends. Enzyme involved in anscription is RNA poly merasse- II, which consists of five polypeptides α,β,β,ω (constitute core enzyme) and σ (sigma (σ) factor). Sigma (σ) factor recognises promoter site while remaining core enzymes take part in chain elongation.