The interaction between DNA and the structural protein IV of bacteriophage PM2 was studied by co-sedimentation, filter binding and electron microscopy. The co-sedimentation data and the sigmoid-shaped filter binding curve were interpreted in terms of co-operative binding. At a given DNA/protein input ratio, some DNA molecules were associated with a large amount of protein IV while others had no detectable protein bound to them. Electron microscopic examination of DNA-protein IV mixtures showed highly condensed DNA molecules alongside uncomplexed native DNA. Dissociation experiments revealed the presence of two types of complexes. Type I dissociated rapidly while type II had a long half-life. Dissociation of complexes obtained with increasing protein/DNA ratios suggested that the type I complex was a precursor of type II complex. Protein IV binds equally well to superhelical, relaxed or linear DNA as well as to single-stranded DNA. These observations lead to a model for the interaction and for the consequent alterations in the DNA structure.
All Science Journal Classification (ASJC) codes
- Molecular Biology