Sequence analysis of bacteriophage T4 DNA packaging/terminase genes 16 and 17 reveals a common ATPase center in the large subunit of viral terminases

Phage DNA packaging is believed to be driven by a rotary device coupled to an ATPase 'motor'. Recent evidence suggests that the phage DNA packaging motor is one of the strongest force-generating molecular motors reported to date. However, the ATPase center that is responsible for generating this force is unknown. In order to identify the DNA translocating ATPase, the sequences of the packaging/terminase genes of coliphages T4 and RB49 and vibriophages KVP40 and KVP20 have been analyzed. Alignment of the terminase polypeptide sequences revealed a number of functional signatures in the terminase genes 16 and 17. Most importantly, the data provide compelling evidence for an ATPase catalytic center in the N-terminal half of the large terminase subunit gp17. An analogous ATPase domain consisting of conserved functional signatures is also identified in the large terminase subunit of other bacteriophages and herpesviruses. Interestingly, the putative terminase ATPase domain exhibits some of the common features found in the ATPase domain of DEAD box helicases. Residues that would be critical for ATPase catalysis and its coupling to DNA packaging are identified. Com binatorial mutagenesis shows that the predicted threonine residues in the putative ATPase coupling motif are indeed critical for function.