Taurocyamine kinase (TK) is a member of the highly conserved family of phosphagen kinases that includes creatine kinase (CK) and arginine kinase. TK is found only in certain marine annelids. In this study we used PCR to amplify two cDNAs coding for TKs from the polychaeteArenicola brasil-iensis, cloned these cDNAs into the pMAL plasmid and expressed the TKs as fusion proteins with the maltose-binding protein.