Linear poly-ubiquitin remodels the proteome and influences hundreds of regulators in <i>Drosophila</i>

Ubiquitin controls many cellular processes via its posttranslational conjugation onto substrates. Its use is highly variable due to its ability to form poly-ubiquitin chains with various topologies. Among them, linear chains have emerged as important regulators of immune responses and protein degradation. Previous studies in Drosophila melanogaster found that expression of linear poly-ubiquitin that cannot be dismantled into single moieties leads to their ubiquitination and degradation or, alternatively, to their conjugation onto proteins. However, it remains largely unknown which proteins are sensitive to linear poly-ubiquitin. To address this question, here we expanded the toolkit to modulate linear chains and conducted ultra-deep coverage proteomics from flies that express noncleavable, linear chains comprising 2, 4, or 6 moieties. We found that these chains regulate shared and distinct cellular processes in Drosophila by impacting hundreds of proteins, such as the circadian factor Cryptochrome. Our results provide key insight into the proteome subsets and cellular pathways that are influenced by linear poly-ubiquitin chains with distinct lengths and suggest that the ubiquitin system is exceedingly pliable.