Produced via a proprietary process resulting in a single rhodamine modification exclusively on the N-terminus of ubiquitin. This site-specific modification results in an ubiquitin that is fully functional at the C-terminus, and with the full compliment of reactive lysines to allow for polyubiquitin chain incorporation. This reagent allows for poly-ubiquitin chain incorporation of rhodamine-N-terminal ubiquitin with higher efficiency and detection sensitivity than traditionally modified ubiquitins.