A bacteriophage is a virus that is able to infect and replicate inside a bacterium host. Catdawg is a mycobacteriophage belonging to Cluster O and the siphoviridae family. GP30, the large terminase protein of Catdawg, is responsible for the cleavage of the DNA and its translocation into the procapsid. There are two components of the large terminase protein which include the ATPase domain and the nuclease domain. The structure of GP30, the large terminase protein is unknown and the amount of structural information on phages is limited. In this study, homology modeling of GP30 was performed and the model was then compared to known crystal structures. The top result was a DNA packaging protein, GP-17 from bacteriophage T4. The predicted structure was then validated using Procheck. These... results confirm that the structure of GP 30, the large terminase protein will contain a similar conformation as the known terminase crystal structures.