Describe the mechanism(s) used by bacteria and eukaryotes for transcription termination
What will be an ideal response?
Bacterial transcription termination can be intrinsic or rho-dependent, and the type of termination is dependent on the presence of certain DNA sequences. In intrinsic termination, inverted repeat DNA sequences followed immediately by a string of adenines produce an mRNA stem-loop followed by a poly-U string. In rho-dependent termination, a rho protein binds to mRNA and catalyzes the release of the transcript from RNA polymerase.
Each of the eukaryotic RNA polymerases uses a different mechanism to terminate transcription. Transcription by RNA polymerase III is terminated in a mechanism that resembles E. coli intrinsic termination. The RNA pol III transcribes a terminator sequence that creates a string of uracils in the transcript. The RNA pol III terminator sequence does not contain an inverted repeat, however, so there is no stem-loop structure near the 3? end of RNA.
Transcription by RNA pol I is terminated at a 17-bp consensus sequence that binds transcription-terminating factor I (TTFI). A large rRNA precursor transcript is cleaved about 18 nucleotides upstream of the TTFI binding site, so the consensus sequence does not appear in the mature transcript.
Termination of transcription by RNA pol II is not completely clear, but it is known that the 3? end
of mRNA is not generated by transcriptional termination. The 3? end of the pre-mRNA is created
by enzymatic action that removes a segment from the 3? end of the transcript and replaces it with a string of adenine nucleotides, the poly-A tail. This step of pre-mRNA processing is thought to be associated with subsequent termination of transcription.
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Answer the following statement true (T) or false (F)
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What will be an ideal response?
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