A- Box plots showing ratios of spliced TT-seq reads over total unspliced and spliced TT-seq reads for all constitutive 5'SSs and 3'SSs detected in major RNA isoforms in RPB1-52R and RPB1-25R cells. p value was calculated using Mann-Whitney U test. Box limits are the first and third quartiles, the band inside the box is the median. The ends of the whiskers extend the box by 1.5 times the interquartile range. Two independent biological replicates were analyzed. B-D- Box plots showing ratios of spliced TT-seq reads over total unspliced and spliced TT-seq reads in RPB1-52R and RPB1-25R cells for all constitutive 5'SSs and 3'SSs detected in major RNA isoforms based on intron position in the transcript: (B) first intron junction, (C) intermediate intron junctions and (D) last intron junctions. p values were calculated using Mann-Whitney U test. Box limits are the first and third quartiles, the band inside the box is the median. The ends of the whiskers extend the box by 1.5 times the interquartile range. 