A DNA-Protein Complex Involved in Bacteriophage phi X174 Particle Formation

A phi X-specific DNA-protein complex has been isolated from phi X-infected cells. This complex contains infective circular single-stranded DNA, the proteins of the genes F, G, H, and J in the same proportions as in the phage particle, and, in addition, the gene D-protein. The D-protein makes up 12-22% of the protein part of the complex. The sedimentation value of the complex is about 140 S. In vitro, the complex can be converted to the normal 114S phage particle (with a concomitant loss of its D-protein) or to an uninfective 70S particle and a small amount of free single-stranded DNA. The fast sedimenting particle is not associated with membranes

The Interaction of the A and A* Proteins of Bacteriophage diX174 with Single-Stranded and Double-Stranded diX DNA in vitro

The binding of the bacteriophage 4X174-coded A and A* proteins to single-stranded (asl>NA) and doublestranded (dsDNA) &X DNA was studied by electron microscopy. The interaction of the A* protein with ssDNA and dsDNA was also studied by sedimentation velocity centrifugation. It was shown that the binding of the A and A* proteins to ssDNA occurs in a non-cooperative manner and requires no or very little sequence specificity under the conditions used here. Both protein-szl )NA complexes have the same compact structure caused by intrastrand cross-linking through the interaction of prolein molecules with separate parts of the ssDNA molecule. The A protein does not bind to 4X dsDNA in the absence of divalent cations. The A' protein does bind to dsDNA, although it has a strong preference for binding to ssDNA. The structure of the A* protein-dsDNA complexes is different from that of the A* protein-ssDNA complexes, as the former have a rosetrc-like structure caused by protein-protein interactions. High ionic strengths favour the formation of large condenwi aggregates