Three sets of experiments (Exp.) were performed in triplicates, and the results are shown in Panels 1 to 3. The original gene names are listed in the leftmost column. M_GBGT1, M_ABO-AB, and H_ABO-A are mouse GBGT1 gene, mouse ABO gene, and the A allele of the human ABO gene, respectively. The tripeptide sequences at the codons corresponding to codons 266 to 268 of human AT/BT are shown in the second column from left. The exon deletions are indicated in the third column. H_ABO-A(Ex 1,2)-M_ABO-AB(Ex 3)-H_ABO-A(Ex 5,6,7) and M_ABO-AB(Ex 1,2)-H_ABO-A(Ex 3,4)-M_ABO-AB(Ex 4,5,6) are human-mouse chimera constructs. The former encodes human AT with exons 3 and 4 replaced by mouse exon 3, and the latter encodes mouse cis-AB transferase with exon 3 replaced by human exons 3 and 4. The results of immunostaining with anti-FORS1 antibody in the triplicate experiments are shown in the next 3 columns. The numbers of cells positive with green fluorescent protein, the expression vector of which was cotransfected, were used to normalize Forssman antigen positivity. The values are shown in percentage of the expression observed of the original mouse FS, M_GBGT1, construct to be 100. The deduced FS activity is also shown semiquantitatively (—, none; +, very weak; ++, weak; +++, moderate; ++++, strong; +++++, very strong activity).