Tetracysteine REASH Reagent *2 mM DMSO Solution*

REASH is a resorufin derivative, modified to contain two arsenic atoms at a set distance from each other. The biarsenical labeling technology works through the high-affinity interaction of arsenic for thiols. When REASH binds to tetracysteine sequences, its biarsenical group reacts rapidly with Cys-Cys moiety and the tag become highly fluorescent in red. The biarsenical labeling reagent REASH is one of the smallest expression tags for labeling a protein that contains a six-amino acid motif with a Cys-Cys-X1-X2-Cys-Cys amino acid sequence. The most commonly used tetracysteine is the six amino acid Cys-Cys-Pro-Gly-Cys-Cys sequence. As this sequence rarely appears in endogenous proteins, incorporating the sequence into target proteins generates a small but highly specific target for protein labeling. REASH generates a strong red fluorescent signal when binding to recombinant proteins containing the tetracysteine motif Cys-Cys-Pro-Gly-Cys-Cys. It can be used for monitoring protein localization, turnover and trafficking, receptor signaling and internalization.