Fluorescent labelling of tRNA and oligodeoxynucleotides using T4 RNA ligase

3'-O-(5'-phosphoryldeoxycytidyl) phosphorothioate and fluorescent 3'-O-(5'-phosphoryldeoxycytidyl) S-bimane phosphorothioate can be ligated to tRNA by T4 RNA ligase. They are also efficient donors for the enzymatic ligation to oligodeoxynucleotides bearing a 3'-cytidine terminus. Cytidine 3',5'-bisphosphate is also a substrate for the ligation reaction with DNA restriction fragments with a 3'-terminate cytidylic acid residue. Oligo- and polynucleotides with a 3'-phosphorothioate group react readily with electrophiles as exemplified by the reaction with monobromobimane.