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During maturation process of some RNA molecules, formation of a 2'–5' phosphodiester bond takes place. Following statements are made about this phenomenon.
(A) Spliceosome mediated removal of intronic sequences occurs through the formation of a 2'–5' phosphodiester bond.
(B) Removal of group II introns occurs through the formation of 2'–5' phosphodiester bond.
(C) Enzymatic removal of introns from the yeast tRNA precursors involves 2'–5' phosphodiester bond formation.
(D) RNaseP mediated 5'-end maturation of tRNA precursors involves formation of a 2'–5' phosphodiester bond.
Which one of the following combinations of the statements is a true representation
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Eduncle Best Answer
In group II introns the reaction pattern is similar except for the nucleophile in the first step, which in this case is the 2’ -hydroxyl group of an A residue within the intron .A branched lariat 2’-5’ structure is formed as an intermediate.
Within the spliceosome, a series of RNA–RNA, RNA–protein, and protein–protein interactions is needed to identify and remove intronic regions and join exons, producing a mature transcript. The mature spliceosome carries out splicing through two transesterification reactions. First, the 2'-OH of a branch point nucleotide performs a nucleolytic attack on the first nucleotide of the intron, forming a lariat intermediate. Second, the 3'-OH from the free exon performs a nucleolytic attack on the last nucleotide of the intron, thereby joining exons and releasing the lariat intron. Intron identification relies on certain sequences, including the 5' splice site, branch point (and downstream polypyrimidine tract) and 3' splice site.