Role of DNA-protein interactions in bacteriophage phi X174 DNA injection.

Like most bacteriophages, phi X174 transfers its DNA through the cell wall, leaving an empty capsid on the cell surface. The process begins with ejection of the genome at its host-receptor site. The rate of this event can be measured, so detailed structure/function analysis of the mechanism is possible now that an atomic structure of the phi X174 protein shell has been obtained. Amino acid substitutions at two arginine residues near the DNA-binding pocket of F capsid protein decrease the eclipse rate, while deletion of 27 bases from the J-F non-coding region increases the rate. An alanine to serine change in the N-terminal region of the phi X174 H "spike" protein has suppressor activity in that this mutation also increases the eclipse rate when the complete genome is present within both mutant and wild-type F capsids. These results suggest that a portion of H protein is inside the capsid, and disruption of DNA-protein interactions is involved in the ejection mechanism.