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FindJunctions operates on RNA-Seq read alignments, using alignments that contain gaps in the read sequence relative to the genomic sequence. These gaps in the read sequence correspond to introns and typically start and end with the so-called canonical splice site consensus sequences "GT" (5' end) and "AG" (3' end) for genes transcribed from the plus (forward) strand. For genes transcribed from the minus (reverse) strand, the consensus sequences relative to the plus strand are the reverse complement of the consensus splice site sequences (i.e., "CT" on the 5' end of the gap and "CAAC" on the 3' prime end).
For each alignment containing a gap, FindJunctions inspects the start and end coordinates of the gap and uses the genomic sequence to infer the strand, if available. FindJunctions creates a list of all such gaps, recording the strand and the genomic coordinates of the start and end coordinates. For each unique triplet of start, end, and strand, FindJunctions creates a scored junction feature and increments the score each time a gap supporting that feature is encountered in a dataset. Options are available to limit scoring to read alignments that have a given minimum number of bases flanking a gap and/or which having one unique mapping onto the genomic sequence.
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