Intrinsic termination
Rho-independent termination is a mechanism in prokaryotes that causes RNA transcription to stop and release the newly made RNA.[1] In this mechanism, the mRNA contains a sequence that can base pair with itself to form a stem-loop structure 7–20 base pairs in length that is also rich in cytosine-guanine base pairs. C-G base pairs have significant base-stacking interactions (especially repeated G-C pairs) and can form three hydrogen bonds between each other, resulting in a stable RNA duplex.[2] Following the stem-loop structure is a chain of uracil residues. The bonds between uracil and adenine are very weak. A protein bound to RNA polymerase (nusA) binds to the stem-loop structure tightly enough to cause the polymerase to temporarily stall.[3] This pausing of the polymerase coincides with transcription of the poly-uracil sequence. The weak adenine-uracil bonds lower the energy of destabilization for the RNA-DNA duplex, allowing it to unwind and dissociate from the RNA polymerase.[4]
Stem-loop structures that are not followed by a poly-uracil sequence cause the RNA polymerase to pause, but it will typically continue transcription after a brief time because the duplex is too stable to unwind far enough to cause termination.
Rho-independent transcription termination is a frequent mechanism underlying the activity of cis-acting RNA regulatory elements, such as riboswitches.
References
- ^ Farnham, PJ; Platt, T (1981-02-11). "Rho-independent termination: dyad symmetry in DNA causes RNA polymerase to pause during transcription in vitro". Nucleic Acids Research. 9 (3): 563–77. doi:10.1093/nar/9.3.563. PMC 327222. PMID 7012794.
- ^ Lewin, Benjamin (2007). Genes IX. Sudbury, MA: Jones and Bartlett Publishers. ISBN 978-0-7637-4063-4.
- ^ Wilson KS, von Hippel PH (September 1995). "Transcription termination at intrinsic terminators: the role of the RNA hairpin". Proc. Natl. Acad. Sci. U.S.A. 92 (19): 8793–7. Bibcode:1995PNAS...92.8793W. doi:10.1073/pnas.92.19.8793. PMC 41053. PMID 7568019.
- ^ Krebs, Jocelyn E.; Goldstein, Elliott S.; Kilpatrick, Stephen T. (2014). Lewin's Genes XI (11th ed.). Burlington, Mass.: Jones & Bartlett Learning. p. 531–533. ISBN 978-1-4496-5985-1.