Precise branch point mapping and quantification of splicing intermediates.

Lariat intermediates of a group II intron were investigated via RT-PCR. Several reverse transcriptases appeared capable of reading through a branched nucleotide. A new method has been established that yields precise information about the location of the branch point within an intron. As an extension of our approach, antisense transcripts of the previously cloned PCR products were successfully used in RNase Protection Assays, providing a tool for quantification of splicing intermediates. Application of the method presented to other self-splicing introns as well as introns in nuclear pre-mRNAs is envisaged.