Dear Editor,The presence and abundance of proteins in the plasma membrane (PM) is regulated by exocytosis and endocytosis.Exocytosis is required for the maintenance of cellular homeostasis following stimulation,whereas endocytosis is important for the reuse and degradation of PM and receptor proteins.Through the specific labeling of proteins on the PM,the process of endocytosis can be tracked and monitored in living cells.Several genetic tags and site-specific labeling approaches that involve the coupling of small organic molecules to tag-fused proteins through either self-labeling or enzymatic ligation have been developed for this purpose (Chen et al.,2005;George et al.,2004;Hoffmann et al.,2010;Keppler et al.,2003;Los et al.,2008;Uttamapinant et al.,2010).However,these methods require a long time for an efficient labeling.