Question

Which of the following statements is incorrect regarding splicing of a Group I intron?

a. Cleavage of the 5’ splice site is induced by a nucleotide within the intron

b. Two transesterifications are involved

c. The RNA of the intron possesses catalytic activity

d. The intron is release as a linear structure

Answer 1

Ans:

a. Cleavage of the 5’ splice site is induced by a nucleotide within the intron

Explanation: Group I intron splicing performs two sequential esterification. In the first step, the 5'-splice site is attacks by 3'-OH of an exogenous (free) guanosine or guanine nucleotide. This reaction adds the G-nucleotideonto the 5'- end of the intron and release 5'-exon. In the 2nd step, 3'-OH of 5'- exon attacks the 3'-splice site phosphodiester bond. This release the intron and ligates the two exon. No lariate structure is formed in this type of splicing and group I intron has autocatalytic activity.