The conjugation of the 76 amino acid protein ubiquitin to other proteins can alter the metabolic stability or non-proteolytic functions of the substrate. Once attached to a substrate (monoubiquitination), ubiquitin can itself be ubiquitinated on any of its seven lysine (Lys) residues or its N-terminal methionine (Met1). A single ubiquitin polymer may contain mixed linkages and/or two or more branches. In addition, ubiquitin can be conjugated with ubiquitin-like modifiers such as SUMO or small molecules such as phosphate. The diverse ways to assemble ubiquitin chains provide countless means to modulate biological processes. We overview here the complexity of the ubiquitin code, with an emphasis on the emerging role of linkage-specific degradation signals (degrons) in the ubiquitin-proteasome system (UPS) and the autophagy-lysosome system (hereafter autophagy).

76个氨基酸的蛋白质泛素与其他蛋白质的缀合可以改变底物的代谢稳定性或非蛋白水解功能。一旦与底物连接（单泛素化），泛素本身就可以在其七个赖氨酸（Lys）残基或其N端甲硫氨酸（Met1）的任何一个上泛素化。单个泛素聚合物可包含混合键和/或两个或多个分支。此外，泛素可以与泛素样修饰剂（如SUMO）或小分子（如磷酸盐）缀合。组装遍在蛋白链的多种方式提供了无数手段来调节生物学过程。我们在这里概述了泛素代码的复杂性，