BIO282 Lecture Notes - Lecture 11: Intrinsic Termination, Stem-Loop, Rho Factor
How does transcription terminate?
• Rho dependent termination
• Rho independent termination
Rho Dependant termination
• Rho factor is a hexamer consisting of 6 identical subunits.
• Rho factor binds at the rut site and moves towards the 3` end.
• Using helicase activity rho unwinds the RNA-DNA hybrid and releases RNA
• Rut - Rho factor utilisation (the site Rho factor recognises
Rho independent termination
• A rho independent terminator is made of an inverted repeat and a run of A’s
• When the inverted repeats are transcribed into RNA, they fold into a hairpin loop.
o This reduced the contact with DNA
• Straight after hairpin loop RNA-DNA hybrid is held together through A-T pairing (weak
hydrogen bonding)
• The weaker pairing destabilizes DNA- RNA hybrid and RNA separates from the template,
terminating transcription.
• The hairpin loop followed by a string of U residues in RNA appear to serve as a signal for the
release of RNA polymerase
Transcription in Eukaryotes
• Eukaryotic cells contain 5 types of RNAPs just for their genomic transcription other than
RNAPs required for transcription in organelles.
• The genomic RNAPs differ in types of genes they transcribe and the number of subunits they
contain
