T4 RNA Ligase 1 (ssRNA Ligase) catalyzes the ligation of a single stranded 5' phosphoryl-termini donor to a 3' hydroxyl-termini nucleic acid acceptor through the formation of a 3'→5' phosphodiester bond, through hydrolysis of ATP to AMP and PPi . Substrates for T4 RNA Ligase I include single-stranded RNA and DNA as well as dinucleoside pyrophosphates.