Figure 2.

Two surface ligation chemistries. (a) Untemplated ligation utilizes T4 RNA ligase to link ssRNA with ssDNA bound on an array surface. (b) Templated ligation uses Taq ligase to conjugate surface-bound oligonucleotide D₂ to oligonucleotide D₁ from solution solely in the presence of complementary oligonucleotide D₃ that forms a surface double-stranded DNA (dsDNA) complex. Ligation will occur only if the nucleotide on the 3′ terminus of D₂ (labeled X) is complementary to the paired nucleotide in D₃.