Expression vector constructs used in transient transfections and purified protein controls. (A) Schematic representation of His10 and His 8 tagged expression vectors with amino acid sequence of attB2 site and His tag shown. (B) Schematic representation of rCD4(d3+4)-His10 tagged expression vector used to express mouse test proteins, amino acid sequence from attB2 site to stop codon (rCD4 sequence has been represented as rCD4) is shown. (C) Schematic representation of His10 tagged expression vector containing signal peptide (SP) at N terminus with amino acid sequence of SP and attB1 site shown. CMV = CMV promoter element, ORF = open reading frame, attB1 = attB1 recombination site, attB2 = attB2 recombination site, rCD4 = rat CD4 domains 3 and 4 tag, His10 = decahistidine tag, His8 = octahistidine tag, stop = stop codon and SP = CD33 signal peptide sequence.