The ligation of peptide hydrazides at a Gly site carrying a removal auxiliary was found to be an efficient process.This technology was successfully used for the synthesis of ubiquitin C-terminal conjugates.Recombinant Ub(1-75)-NHNH2 was prepared through the hydrozinolysis of the Ub(1-75)-intein fusion protein.It was ligated with a glycine derivative modified with an acid-sensitive thiol auxiliary.The final acid treatment produced the desired bioactive ubiquitin conjugates in practical quantities.Thus the method described here extends the protocols of expressed protein ligation.