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Transcription Terminator 音乐资讯in Prokaryotes
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北京特产In genetics, a transcription terminator is a ction of nucleic acid quence that marks the end of a gene or operon in genomic DNA during transcription. This quence mediates transcriptional termination by providing signals in the newly synthesized transcript RNA that trigger process which relea the transcript RNA from the transcriptional complex. The process include the direct interaction of the mRNA condary structure with the complex and/or the indirect activities of recruited termination factors. Relea of the transcriptional complex frees RNA polymera and related transcriptional machinery to begin transcription of new mRNAs.
Two class of transcription terminators, Rho-dependent and Rho-independent, have been identified throughout prokaryotic genomes. The widely distributed quences are responsible for triggering the end of transcription upon normal completion of gene or operon transcription, mediating early termination of transcripts as a means of regulation suc蜜坛
h as that obrved in transcriptional attenuation, and to ensure the termination of runaway transcriptional complexes that manage to escape earlier terminators by chance, which prevents unnecessary energy expenditure for the cell.
Rho-dependent terminators:
Rho-dependent transcription terminators require a protein called Rho factor, which exhibits RNA helica activity, to disrupt the mRNA-DNA-RNA polymera transcriptional complex. Rho-dependent terminators are found in bacteria and phage. The Rho-dependent terminator occurs downstream of translational stop codons and consists of an unstructured, cytosine-rich quence on the mRNA known as a Rho utilization site (rut) for which a connsus quence has not been identified, and a downstream transcription stop point (tsp). The rut rves as a mRNA loading site and as an activator for Rho; activation enables Rho to efficiently hydrolyze ATP and translocate down the mRNA while it maintains contact with the rut site. Rho is able to catch up with the RNA polymera, which is stalled at the downstream tsp sites. Contact between Rho and the RNA polymer
a complex stimulates dissociation of the transcriptional complex through a mechanism involving allosteric effects of Rho on RNA polymera.
Rho-independent terminators:
Intrinsic transcription terminators or Rho-independent terminators require the formation of a lf-annealing hairpin structure on the elongating transcript, which results in the disruption of the mRNA-DNA-RNA polymera ternary complex. The terminator quence in DNA contains a 7-20 bapair GC-rich region of dyad symmetry followed by a short poly-T tract or "T stretch" which is transcribed to form the terminating hairpin and a 7–9 nucleotide "U tract" respectively. The mechanism of termination is hypothesized to occur through a combination of direct promotion of dissociation through allosteric effects of hairpin binding interactions with the RNA polymera and "competitive kinetics". The hairpin formation caus RNA polymera stalling and destabilization, leading to a greater likelihood that dissociation of the complex will occur at that location due to an incread time spent paud at that site and reduced stability of the complex. Additionally,
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the elongation protein factor NusA interacts with the RNA polymera and the hairpin structure to stimulate transcriptional termination.
Simplified schematics of the mechanisms of prokaryotic transcriptional termination in vector version. Rho-independent termination, a terminating hairpin forms on the nascent mRNA interacting with the NusA protein to stimulate relea of the transcript from the RN
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A polymera complex (top). In Rho-dependent termination, the Rho protein binds at the upstream rut site, translocates down the mRNA, and interacts with the RNA polymera complex to stimulate relea of the transcript (bottom).
A predicted conrved condary structure and quence conrvation annotation for 90 bacterial Rho-independent termination elements.
