Factor Xa cleavage of fusion proteins. Elimination of non-specific cleavage by reversible acylation.

A method is described for the elimination of non-specific cleavage of fusion proteins by factor Xa. Putative non-specific cleavage sites C-terminal to lysyl residues are blocked by reversible acylation by 3,4,5,6-tetrahydrophthalic anhydride prior to cleavage. After cleavage, the acyl groups are removed quantitatively by exposure to slightly acidic conditions. This method employs no harsh reagents or conditions, and may be generally applicable to factor Xa cleavage of fusion proteins.