RNA polymerase 3

Function

• synthesizes small RNAs, including: tRNA, 5SrRNA, 7SK RNA & U6 snRNA
• a single stranded DNA template strand of the promoter is positioned within the central active site cleft
• a bridging helix emanates from POLR3A & crosses the cleft near the catalytic site & is thought to promote translocation of RNA polymerase 3 by acting as a ratchet that moves the RNA-DNA hybrid through the active site by switching from straight to bent conformations at each step of nucleotide addition (putative)
• components of RNA polymerase 3 have a role in sensing & limiting infection by intracellular bacteria & DNA viruses
  • act as nuclear & cytosolic DNA sensor involved in innate immune response
  • can sense non-self dsDNA that serves as template for transcription into dsRNA
  • the non-self RNA polymerase 3 transcripts, such as Epstein-Barr virus-encoded RNAs (EBERs) induce type 1 interferon & NF- Kappa-B through the RIG-I pathway

Structure

• consists of about 17 subunits
• RPC3/POLR3C, RPC6/POLR3F & RPC7/POLR3G form a RNA polymerase 3 subcomplex

More general terms

• RNA polymerase

Components

• DNA-directed RNA polymerase III subunit RPC5; RNA polymerase III subunit C5; DNA-directed RNA polymerase III 80 kD polypeptide (POLR3E, KIAA1452)
• DNA-directed RNA polymerase III subunit RPC2; RNA polymerase III subunit C2; C128; DNA-directed RNA polymerase III 127.6 kD polypeptide; DNA-directed RNA polymerase III subunit B (POLR3B)
• DNA-directed RNA polymerase III subunit RPC8; RNA polymerase III subunit C8; DNA-directed RNA polymerase III subunit H; RNA polymerase III 22.9 kD subunit; RPC22.9 (POLR3H, KIAA1665, RPC8)
• DNA-directed RNA polymerase III subunit RPC6; RNA polymerase III subunit C6; DNA-directed RNA polymerase III subunit F; RNA polymerase III 39 kD subunit; RPC39 (POLR3F)
• DNA-directed RNA polymerase III subunit RPC3; RNA polymerase III subunit C3; DNA-directed RNA polymerase III subunit C; RNA polymerase III 62 kD subunit; RPC62 (POLR3C)
• DNA-directed RNA polymerase III subunit RPC4; RNA polymerase III subunit C4; DNA-directed RNA polymerase III subunit D; DNA-directed RNA polymerase III 47 kD polypeptide; RPC53; protein BN51 (POLR3D, BN51, BN51T)