ST6GAL1 and infection: A selectivity index plot (ST3/ST6 infection efficiency at 1 particle/cell) shows (Figure S6) that relative infection levels supported by ST3Gal4 or ST6Gal1 matched previously determined13 relative affinities for 2-3 sialyllactosamine and 2-6 sialyllactosamine (KD 2–6/KD2-3).