fixStartStop.feat(x)
feat
. CDS regions must be present with type
"CDS", and the transcript_id must be indicated in the attribute field.
Start and stop codons should have feature type "start_codon" and "stop_codon"
(as produced by addSignals.feafeat
, in which CDS regions are ensured to
include start codons and exclude stop codons, as required by the GTF2 standard.