text: Transcription attenuation is a type of prokaryotic regulation that happens only under certain conditions. This process occurs at the beginning of RNA transcription and causes the RNA chain to terminate before gene expression. Transcription attenuation is caused by the incorrect formation of a nascent RNA chain. This nascent RNA chain adopts an alternative secondary structure that does not interact appropriately with the RNA polymerase.  In order for gene expression to proceed, regulatory proteins must bind to the RNA chain and remove the attenuation, which is costly for the cell.
  In prokaryotes there are two mechanisms of transcription attenuation. These two mechanisms are intrinsic termination and factor-dependent termination.
  - In the intrinsic termination mechanism, also known as Rho-independent termination, the RNA chain forms a stable transcript hairpin structure at the 3end of the genes that cause the RNA polymerase to stop transcribing. The stem-loop is followed by a run of Us (poly U tail) which stalls the polymerase, so the RNA hairpin have enough time to form. Then, the polymerase is dissociated due to the weak binding between the poly U tail, from the transcript RNA, and the poly A tail, from the DNA template, causing the mRNA to be  prematurely released. This process inhibits transcription. To clarify, this mechanism is called Rho-independent because it does not require any additional protein factor as the factor-dependent termination does, which is a simpler mechanism for the cell to regulate gene transcription.  Some examples of bacteria where this type of regulation predominates are Neisseria, Psychrobacter and Pasteurellaceae, as well as the majority of bacteria in the Firmicutes phylum.
  - In factor-dependent termination, which is a protein factor complex containing Rho factor, is bound to a segment from the RNA chain transcript. The Rho complex then starts looking in the 3 direction for a paused RNA polymerase. If the polymerase is found, the process immediately stops, which results in the abortion of RNA transcription. Even though this system is not as common as the one described above, there are some bacteria that uses this type of termination, such as the tna operon in E.coli'.
  This type of regulation is not efficient in eukaryotes because transcription occurs in the nucleus while translation occurs in the cytoplasm. Therefore, the mechanism is not continued and it cannot execute appropriately as it would if both processes happen on the cytoplasm.