Question

A researcher is studying introns in a gene of interest. She notes that in a subpopulation of her cells, “Intron 1” of the gene completely lacks an “AG” sequence. This would likely result in which of the following?

	A.	Failure of any snRNPs to bind to the branch point of the intron
	B.	Failure of the lariat (and intron) to be removed during splicing
	C.	Failure of a lariat to even form during splicing of this intron
	D.	Failure of the 5' splice site to be cut

Answer 1

The correct option for this question is option 'B' i.e. failure of the lariat (and intron) to be removed during splicing. It is explained below.

This is case of GU-AG intron splicing. There are two main events in this splicing. One is Assembly of spliceosome and other is transesterification reaction. There are two transesterification reactions. First transesterification reaction is between 2' OH of Branch point (A) and 5' - splice site (GU). The second transesterification reaction occurs between 3' OH of exon and 3' splice site (AG). The whole mechanism occurs like this: So, if "AG" sequence of 3' splice site are missing , then it is not possible for 2^nd transesterification reaction to occur properly and thus lariat (and intron) can't be removed during splicing.