The diagram shown here is part of an RNA transcript containing four open reading frames (M, H, K, and L) and three introns (1, 2, 3). The sites labeled d1-d3 are nucleotides immediately before each intron on the 5' side and those labeled a1-a3 are nucleotides immediately after each intron on the 3' side. Splicing out an intron involves a spliceosome facilitating the cleavage of the DNA at the d and a sites at either end of the intron. How many processed transcripts are possible in which two d sites and two a sites are cleaved?

Question

The diagram shown here is part of an RNA transcript containing four open reading frames (M, H, K, and L) and three introns (1, 2, 3). The sites labeled d1-d3 are nucleotides immediately before each intron on the 5' side and those labeled a1-a3 are nucleotides immediately after each intron on the 3' side. Splicing out an intron involves a spliceosome facilitating the cleavage of the DNA at the d and a sites at either end of the intron.  How many processed transcripts are possible in which two d sites and two a sites are cleaved?

Quizplus · Accepted Answer

If two d sites and two a sites are cleaved, introns 1 and 3 will be spliced out, leaving only the exon between them. The potential transcripts are:
-MHKL (no splicing)
-MH-L (splice out intron 1)
-M-KL (splice out intron 3)
-M-L (splice out introns 1 and 3)

Therefore, there are two possible processed transcripts.

The Diagram Shown Here Is Part of an RNA Transcript