Which of the following is most likely attributable to a base substitution at a 5' splice junction? View Available Hint(s) Which of the following is most likely attributable to a base substitution at a 5' splice junction? A shorter than usual final transcript A longer than usual final transcript An amino acid substitution in the final protein product Failure of the U2 snRNP to bind the transcript

The sequence of 5' end of splice junction is the site to start the process of splicing. The spliceosomal introns have GU at 5' end and AG at 3' end. These sequences mark the site where splicing occurs. The snRNA contains a sequence complementary to sequences near the 5' splice site of nuclear mRNA introns and facilitates the binding of snRNP to this sequence in the primary transcript to start the process of splicing.

In the case of group I introns, the 3'-OH end of guanosine does a nucleophilic attack at the phosphate present at "U" of 5' splice site. Now, the 3'-OH of the 5' exon serves as a nucleophile and removes the intron. Any substitution in 5' sequence of splice junction would not allow the 3'-OH to do a nucleophilic attack on it and the intron will not be removed leading to a longer final transcript that the one formed by original primary transcript.