Ligand-directed crosslinking of DNA to CAII. (A) Structures of reactive groups (RG) (tosyl 1, NHS ester 2, sulfonyl fluoride 3, phenyl azide 4, diazirine 5). (B) Structure of 5′-GL-CBS-ssDNA hybridized to 3′-reactive group-5′-FAM-ssDNA′. (C) SDS-PAGE analysis of reactive group crosslinking efficiencies with GL-CBS ligand to CAII (10 μM CAII, 10 μM BSA, 1.0 μM ligand-ssDNA, 0.75 μM RG-ssDNA′). Crosslinking yields were determined from ratio of the FAM fluorescence of crosslinked CAII (CAII-DNA) to the total crosslinked and non-crosslinked 5′-FAM-ssDNA (DNA).