Notes on RNA Transcription Termination

Overview

• RNA polymerase stops transcription at specific sites called transcription terminators.
• These terminators are encoded by DNA but function at the RNA level.

Row-independent Transcription Termination

• Requires no accessory proteins.
• Stem-loop structure:
  • Formed by intrastrand base pairing within the RNA.
  • Consists of complementary bases forming hydrogen bonds, creating a secondary RNA structure.
  • Often followed by a series of uridines in the RNA.
• Mechanism:
  • Uridines in RNA interact with adenines in DNA, forming weak hydrogen bonds.
  • As RNA polymerase encounters the stem-loop, it pauses and dissociates, releasing the mRNA.
  • RNA polymerase can then find another promoter and restart transcription.

Row-dependent Transcription Termination

• Involves the Greek letter Rho (ρ).
• Requires accessory proteins.
• Mechanism:
  • RNA contains a Rho utilization site (RUT), which is a sequence where Rho protein can bind.
  • Rho is a helicase that, upon binding to RUT, moves towards the RNA complex, causing separation of the DNA and RNA strands.
  • This separation releases RNA and RNA polymerase from DNA, ending transcription.
  • Rho protein can continue to bind to other RUT sequences and assist in termination.

Transcription in Different Domains

• The process described concludes transcription in bacteria.
• Archaea and eukaryotic transcription is more complex.
• Eukaryotic RNA processing:
  • Introns must be removed before RNA can exit the nucleus for translation.

Summary

• Two primary types of transcription termination: row-independent and row-dependent.
• Each mechanism involves specific structures and processes to halt transcription and release RNA for further processing or translation.