Question

3. Two RNA sequences that can cause premature transcription termination are the trp leader sequence (trp L) in E. coli and the thi riboswitch in B. subtilis. For each of these RNAs, discuss how alternate secondary structures impact termination and describe the conditions that favor each of the alternate secondary structures.

Answer 1

Answer:

As per the data- Two RNA sequences that can cause premature transcription termination are the trp leader ............

• Trp L causes the attenuation by premature transcription at the attenuator site which is located downstream from the promoter operator region and are located ahead of the coding sequences for the trp enzymes.
• For trp mRNA , the charged tryptophan results in attenuation of the trp operon with changes in the structure of leader sequence. The region 2 sequence can either base pair with region 1 or region 3 or region 3 could base pair with either region 2 or region 4 .
• Region 1 contains 2 codons for tryptophan binding. If tryptophan is in sufficient quantity, the ribosome would translate the leader sequence following melting of region 1 and region 2 base pairs.
• Synthesis of region 3 and 4 form a stem loop succeeding a series of U residues, for transcription termination without the rho mechanism.

Riboswitch mechanism of Bacillus subtilis.

• The FMN riboswitch is a conserved RNA domain, which is also known as the RFN element , which is found in the 5' UTR, untranslated regions, in the prokaryotic mRNAs.
• This element would bind directly to the FMN, and is a metabolite dependent riboswitch which controls the gene expression by premature transcription termination.
• This would happen within the 5' UTR region of the B.subtilis. This is also a Rho independent mechanism which results in folding sequesters inhibiting translation.

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