sentence: NPr - ( His ) and NPr ( H16A ) - ( His ) expressed from these plasmids consist of the complete NPr sequence plus the additional residues LEHHHHHH at the C-terminus.To purify NPr and SixA proteins with cleavable polyhistidine tags , genes were cloned into the pET-41 vector backbone using NEBuilder HiFi DNA Assembly ( New England BioLabs ) .