Question

How many types of RNA polymerases exist in cells? Write their names and functions.

Answer 1

• An RNA polymerase (RNAP), or ribonucleic acid polymerase, is a multisubunit enzyme that catalyzes the process of transcription in which an RNA polymer is synthesized from a DNA template.
  
• Prokaryotic RNA polymerase is made of four subunits including a sigma-factor that dissociates from the enzyme complex after transcription initiation. While prokaryotes use the same RNA polymerase to catalyze the polymerization of coding as well as non-coding RNA, the eukaryotes have five distinct RNA polymerases.
  
• Eukaryotic RNA polymerase - I produce nearly fifty per cent of the RNA transcribed in the cell. It exclusively polymerizes ribosomal RNA.
  
• RNA Polymerase - II is extensively studied because it is involved in the transcription of mRNA precursors. It also catalyzes the formation of small nuclear RNAs and micro RNAs.
  
• RNA polymerase - III transcribes transfer RNA, some ribosomal RNA and a few other small RNAs and is important since many of its targets are necessary for normal functioning of the cell.
  
• RNA polymerases IV and V are found exclusively in plants, and together are crucial for the formation of small interfering RNA and heterochromatin in the nucleus.