If the sequence of the portion of the U6 snRNA that is involved in interactions

Question

If the sequence of the portion of the U6 snRNA that is involved in interactions with the U2 snRNA is changed from 5' UGAUCAGC 3' to 5' AGAUGACG 3', what specific step in splicing would be blocked? Suggest a compensatory mutation in U2 snRNA (a mutation that would restore splicing in combination with the U6 mutant). Grading: for describing the specific step of splicing that would be blocked. for the sequence of the U2 snRNA compensatory mutant (1 pt deducted if 5' and 3' ends are not correctly labeled).

Explanation / Answer

i) We know that binding of U6 to U2 catalyses transesterification making the 5’ end of the intron ligate to the A on the intron and form a lariat.

Thus any sort of mutation in U6 or U2 result in the blocking of the transesterification step, which means that lariat formation will not occur.

ii) Sequence of U2 snRNA compensatory mutant:

3’ – UCUACUGC – 5’

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