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what an RNA pseudoknot is. Briefly show how are they involved in frame-shifting, IRES recognition and telomerases.

MY QUESTION IR RELATED TO BIOCHEMISTRY AND it WAS DISCUSSED IN THE ARTICLE "Unraveling the structural complexity in a single-stranded RNA tail: implications for efficient ligand binding in the prequeuosine
riboswitch" by  Catherine D. Eichhorn1, Jun Feng2,3, Krishna C. Suddala2,3, Nils G. Walter2, Charles L. Brooks and Hashim M. Al-Hashimi . I WOULD BRIEF ANSWER  FOR THE QUESTION E ?
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1 Answer

Hi Sawsan
Pseudoknot is an architectural RNA element that is sometimes formed by a hanging single stranded RNA and the neighboring hairpin of another RNA. When a ribosome is translating RNA for protein synthesis and comes to pseudoknot, it fails to translated as the triplet is blocked by pseudoknot formation. Ribosome moves to next base/codon and a frameshift occurs.
For IRES recognition by ribosome, a pseudoknot upstream of AUG codon  appears essential for translation. Mutational analysis abolishing the pseudoknot structure results in reduction of translation. This is shown by Wang et al, 1995.
Pseudoknot is a conserved RNA component of telomerase, its disruption in tetrahymena telomerase RNA prevents  in vivo assembly of telomerase. Blackburn group has shown this.
Hope this helps.