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Intrinsic termination (rho-independent) relies on a stable hairpin with a subsequent uridine repeat. The common explanation on how these sequences cause the termination of the transcription are based on the thermodynamic stability of the sequence. The GC-rich stable hairpin together with the destabilizing U-repeat supposedly destabilize the binding of the polymerase enough to cause it to disassociate from the template.

What I'm looking for are specific requirements on the termination sequences that are not based on thermodynamics.

  • Are there any specific requirements on the hairpin sequence beyond a certain thermodynamic stability.
  • Are there any loop variants that are known to reduce the termination efficiency?
  • Does the shape of the hairpin, e.g. any kinks or bulges in it, have an influence on termination efficiency?

The typical requirements I read are 5-14bp and GC-rich, and I'd like to know if there are any more specific requirements, especially ones related to the structure and not the stability of the hairpin.

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The RNA hairpin transcription terminator in prokaryotes is terminated by the GC rich hairpin followed by 4+ uracil bases as you describe it.

The original reference describing the hairpin, described the sequence requirements as being for the thermodynamic stability of the hairpin, but the protein nusA has also been found to stimulate termination.

You might think that there would be some protein that would precisely bind this motif and mediate the termination, but at least as far as I can find, it appears that the hairpin clogs up the polymerase itself, causing termination. This review linked here has some nice pictures of the RNAP bindig pocket model.

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