The enzyme DNA ligase catalyzes the template-driven condensation of the 3'-hydroxyl group of one DNA strand with the 5'-monophosphata group of a second DNA strand. As part of a study of DNA ligase, we required a method for 5'-phosphorylation of an oligonucleotide during phosphoramidite-based, automated DNA synthesis.'Fur-thermore, this phosphorylated oligonucleotide needed to be separable, by reversed-phase HPLC, from ...