Recent analyses of mammalian RNAs have revealed the translation of numerous short open reading frames (sORFs). However, it is unknown whether these translation events produce stable polypeptide products that persist in the cell at functionally relevant concentrations. To address this question, we developed a mass spectrometry-based strategy to directly detect sORF-encoded polypeptides (SEPs) in human cells. This analysis identified 111 novel SEPs, which is the largest number of human SEPs ever reported. We observed widespread translation of SEPs from non-canonical RNA contexts, including polycistronic mRNAs and sORFs defined by non-AUG start codons. In addition, coding sORFs were present in a small fraction (10/1866) of long intergenic non-coding RNAs (lincRNAs). Lastly, we find that SEPs exhibit subcellular localization and engage in protein-protein interactions, which demonstrates that SEPs share key attributes with functional proteins. Together, these results provide the strongest evidence to date that coding sORFs constitute a significant human gene class.

Discovery and characterization of human short ORF-encoded polypeptides

244th National Meeting (2012)

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