Thermostable USER® III Enzyme

A thermolabile version is also available, Thermolabile USER II Enzyme (NEB #M5508).

We are excited to announce that all reaction buffers are now BSA-free. NEB began switching our BSA-containing reaction buffers in April 2021 to buffers containing Recombinant Albumin (rAlbumin) for restriction enzymes and some DNA modifying enzymes. Find more details at


Thermostable USER (Uracil-Specific Excision Reagent) III Enzyme generates a single nucleotide gap at the location of a uracil residue. It is active between 50-75°C (optimal activity observed at 65°C).

Figure 1: Thermostable USER III Enzyme

Afu Uracil DNA glycosylase (UDG) catalyzes the excision of a uracil base, forming an abasic (apyrimidinic) site while leaving the phosphodiester backbone intact. The lyase activity of Endonuclease IV breaks the phosphodiester backbone at the 3′ and 5′ sides of the abasic site so that base-free deoxyribose is released.

Catalog # Concentration Size List Price Your Price Quantity
M5509S 1,000 units/ml 50 units $104.00
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