The Ubiquitin-Proteasome System (UPS) regulates many cellular processes in eukaryotic cells. Ubiquitylation by the UPS mainly directs proteins to proteasomal degradation, but it can also have non-degradative functions, such as regulating protein activity or localization. The small protein ubiquitin is conjugated to its substrates via a cascade of E1-E2-E3 enzymes. Dysregulation of the UPS has been implicated in the genesis and progression of many diseases, such as neurodegenerative diseases and cancer; thus, the UPS components are attractive targets for developing pharmaceutical drugs. E2s, or ubiquitin conjugating enzymes, are central players of the UPS. E2s function in tandem with specific ubiquitin ligases (E3s) to transfer ubiquitin to substrates. Here, we present the first proteome stability analysis of two closely related ubiquitin conjugating enzymes, UBC4 and UBC5, in S. cerevisiae. These two E2s are nearly identical, having 92% sequence identity and differing by only 11 amino acid residues. This dataset is of broad interest because higher eukaryotes express ubiquitin conjugating enzymes that are analogous to the yeast UBC4/5.