A Structural and Evolutionary Analysis of the Bacteriophage Head-tail Connector

Macromolecular complexes are important in almost all cellular processes. The bacteriophage head-tail connector complex offers a model with which to study the mechanisms that control their formation and the interactions that govern their assembly. The head-tail connector joins DNA-filled heads with mature tails. This thesis describes the structures, functions, and evolution of two connector proteins, HK97 gp6 and lambda gpFII. Middle-ring connector proteins act as head-stabilizing proteins after the packaging of DNA in the heads. I found that gp6 is the middle-ring connector protein of bacteriophage HK97. I determined that gp6 is part of a large family of middle-ring connector proteins that share common sequence and structure elements. I also show that the mechanism for the addition of gp6 to the connector is mediated by limiting gp6 expression by strictly controlling translation initiation. I also describe a three-dimensional model for the assembly of the head-tail joining protein of bacteriophage lambda, gpFII. This model correctly predicts regions of the protein predicted to interact with the lambda head and tail. It also provides evidence for the description of a new family of proteins that evolved from a tail tube protein. This family includes members from both contractile and non-contractile phage tails and the bacterial type VI secretion system.