The novel feature of APPRIS is that it selects a principal isoform for each gene based on the reliable annotations for protein structure, function and cross-species conservation. The principal isoform is the representative isoform of the gene, the isoform against which all other (alternative) isoforms should be compared. In APPRIS, the principal isoform is the isoform with the main cellular function, the isoform that is expressed in the majority tissues or in most stages of development or the isoform that is the most evolutionary conserved. The process of selecting principal isoforms is illustrated with biologically relevant examples in the ‘APPRIS annotation’ section.
