Identification and Validation of ISG15 Target Proteins.

ISG15 is an interferon-induced ubiquitin-like protein (Ubl) that has antiviral properties. The core E1, E2 and E3 enzymes for conjugation of human ISG15 are Ube1L, UbcH8 and Herc5, all of which are induced at the transcriptional level by Type 1 interferon signaling. Several proteomics studies have, together, identified over 300 cellular proteins as ISG15 targets. These targets include a broad range of constitutively expressed proteins and approximately 15 interferon-induced proteins. This chapter provides an overview of the target identification process and the validation of these targets. We also discuss the limited number of examples where the biochemical effect of ISG15 conjugation on target proteins has been characterized.