Discovery of Human sORF-Encoded Polypeptides (SEPs) in Cell Lines and Tissue

The existence of nonannotated protein-coding
human short open reading
frames (sORFs) has been revealed through the direct detection of their
sORF-encoded polypeptide (SEP) products. The discovery of novel SEPs
increases the size of the genome and the proteome and provides insights
into the molecular biology of mammalian cells, such as the prevalent
usage of non-AUG start codons. Through modifications of the existing
SEP-discovery workflow, we discover an additional 195 SEPs in K562
cells and extend this methodology to identify novel human SEPs in
additional cell lines and human tissue for a final tally of 237 new
SEPs. These results continue to expand the human genome and proteome
and demonstrate that SEPs are a ubiquitous class of nonannotated polypeptides
that require further investigation.