RNA Polymerase (RNAP)

RNA  Polymerase (RNAP)

1. RNA polymerase (ribonucleic acid polymerase), both abbreviated RNAP or RNApol, official name DNA-directed RNA polymerase, is a member of a family of enzymes that are essential to life.
2. RNAP locally opens the double-stranded DNA (usually about four turns of the double helix) so that one strand of the exposed nucleotides can be used as a template for the synthesis of RNA, a process called transcription.

• They  are  DNA dependent  RNA Polymerase.
• No primer is  needed  in  RNAP
• No proofreading  activity in  RNAP.
• Prokaryotic  RNA polymerase  is of only one type.
• There  are three  types  of Eukaryotic  RNA Polymerase,  RNA  Polymerase  I, II and III.
• Bacterial RNAP enzyme contains two alpha, two beta subunits, one omega subunit, and one sigma factor and two zinc molecules.
• RNAP type II or Bis the main enzyme synthesizing mRNAs. It is inhibited by alpha-amanitin.
• Phosphorylation activates RNAP II.
• RNAP type I or A is responsible for the synthesis of Rrna (ribosomal); it is not inhibited by amanitin.
• RNAP type III or C is responsible for the production of tRNA; it is moderately sensitive to amanitin.
• RNAP type III catalyzes the synthesis of flRNA, small nuclear RNA (sz-RNA) and miRNA
• Sigma factor enables the holoenzyme (RNA polymerase) to recognize and bind to The promoter sequence. Different sigma (σ) factors recognize the different group of genes
• Alpha-amanitin inhibits RNA  polymerase  II of eukaryotes.
• Rifampicin inhibits b-subunit of RNA  polymerase.
• RNA polymerase (holoenzyme)= core enzyme+ sigma subunit
• RNA  polymerase  holoenzyme requires:

1. A template of ds/ss DNA
2. Four ribonucleotide triphosphates GTP, UTP, ATP, CTP
3. Mg” or Mn”

• RNA primers are required for DNA replication, not for transcription.
• RNA  polymerase is The major enzyme involved in transcription.