Use1 is a recently identified E2 conjugating enzyme which is specifically charged with ubiquitin by an alternate E1 activating enzyme Uba6 (E-307). Uba6 has a distinct preference and specificity for Use1 based on the regions specific to the C-terminal ubiquitin-fold domain. Use1 is not active with the canonical ubiquitin E1 (UBE1, E-305). After activating ubiquitin, Uba6 transfers ubiquitin to Use1 leading to the formation of a thiolester linkage with its catalytic site cysteine (Cys¹⁸⁸). The ubiquitin can then be conjugated to substrate proteins via specific E3 ligase enzymes. This protein contains an N-terminal His₆ tag.