Ubiquitin chains in the Dsk2 UBL domain mediate Dsk2 stability and protein degradation in yeast

► We show that the UBL domain of Dsk2 is ubiquitinated in yeast. ► Dsk2 that is defective in the UBA domain is unstable. ► Depending on Ub chains, the UBA-defective Dsk2 is degraded by Ub–proteasome pathway. ► Dsk2 ubiquitination affects Ub-dependent protein degradation in vivo. ► Ub chains of UBL domain mediate Dsk2 own stability and protein degradation in yeast. Ubiquitin-like (UBL)–ubiquitin-associated (UBA) proteins, including Dsk2 and Rad23, act as delivery factors that target polyubiquitinated substrates to the proteasome. We report here that the Dsk2 UBL domain is ubiquitinated in yeast cells and that Dsk2 ubiquitination of the UBL domain is involved in Dsk2 stability, depending on the Dsk2 UBA domain. Also, Dsk2 lacking ubiquitin chains impaired ubiquitin-dependent protein degradation and decreased the interaction of Dsk2 with polyubiquitinated proteins in cells. Moreover, Dsk2 ubiquitination affected ability to restore the temperature-sensitive growth defect of dsk2Δ. These results indicate that ubiquitination in the UBL domain of Dsk2 has in vivo functions in the ubiquitin–proteasome pathway in yeast.