I am working on denovo genome annotation, I need to build a GFF3 annotation file starting from a set of CDS exported from Artemis. My problem is that when I export the CDS features from Artemis (say into FASTA format), it doesn't include the reading frame of each CDS.

Is there a feature in Artemis that I've missed that can do this automatically ? Otherwise, any ideas how I can deduce the reading frame from CDS start and end coordinates only ?

PS : I've tried looking at 'cds_start_position % 3' values with no success so far.

Cheers :)