What nucleotide does the branch point nucleotide bind in order to form the lariat intermediate? What...

What nucleotide does the branch point nucleotide bind in order to form the lariat intermediate? What is unusual about the bond between these two nucleotides?

Expert Solution

What nucleotide does the branch point nucleotide bind in order to form the lariat intermediate? What is unusual about the bond between these two nucleotides?

Brach point sequences are located on the upstream of 3′ end of an intron and the size varies from18 to 40 nucleotides. Though it is loosely consrved, adenine always remains. Spliceosome is responsible for the unusual 2′,5′-phosphodiester linkages in RNA lariats. The unusual linkage has to be hydrolyzed by the enzyme called intron debranching enzyme (Dbr1).This step is a rate limiting step and required for the process and efficient maturation of essential cellular factors such as small nucleolar RNAs (snoRNA) and micro RNAs (mirtrons). Spliceosomal splicing is a two step sequential transesterification reactions:

Lariat intermediate formed by the nucleophilic attack initiated by 2'OH of a specific branchpoint nucleotide within the intron on the first nucleotide of the intron at the 5' splice site.
Electrophilic attack at last nucleotide of the intron at the 3' splice site which is followed by first nucleotide due to 3'OH of released 5' exon and thus releases the lariant intron while joining exons.

gladiator answered 2 years ago

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