Protein Encoding Gene. Protein encoding gene (PEG), protein coding sequence (CDS), and open reading frame (ORF) are nearly synonymous terms. In the FIG ID, the feature type for a protein encoding gene is.Protein encoding genes are commmonly described as structural or regulatory. Structural genes encode enzymes and structural proteins.rotein Encoding Gene. Protein encoding gene (PEG), protein coding sequence (CDS), and open reading frame (ORF) are nearly synonymous terms. In the FIG ID, the feature type for a protein encoding gene is.