interpret circRNA coordinate

[frankligy]

Hello,

Thanks so much for developing this wonderful tool! I would like to confirm if my interpretation of circExplorer2-reported circRNA coordinates are correct?

So after a few manual inspections of the reported circRNA including the ones on the CIRCpedia database, my understanding is as below:

If the reported coordinate is like that chr1:400-500, depending on the strand, if the strand='+', it means the first exon ends at position 500, and then circle back to the upstream exon at position 401. If the strand='-', it means the first exon ends at position 401, and then circle back to the upstream exon at position 500.

Am I understanding correctly, the +1 seems to be necessary as the reported first coordinate in the text file is always the last nt in the intron instead of first nt in the exon. As the document said, all the reported circRNA in known_circRNA have to be consistent with exon boundary. That's how I derived my interpretation. I didn't find any other detailed explanation, that's why I want to confirm here.

Thanks in advance,
Frank