title: DNA and protein lattice-lattice interactions in the filamentous bacteriophages.
abstract: The relations between the protein coats and DNAs of the four filamentous bacteriophages fd, Xf, Pf1, and Pf3 are considered. These viruses have similar morphologies, yet show a diversity of detailed structure, having different protein coat symmetries (helical and rotational), different coat protein sizes (44-50 amino acids per subunit) and sequences, different nucleotide axial translations (2.3-5.5 A), and different ratios of nucleotides per coat protein subunit (integers 1.0 and 2.0, and nonintegers approximately 2.4). These divergences are all reconciled quantitatively by means of two theoretical concepts: the pitch connection and the restricted pitch connection. The pitch connection relates protein and DNA surface lattices with arbitrary, nonintegral nucleotide/subunit ratios in a nonrandom way. The restricted pitch connection selects a preferred set of n/s values. Both relations are derived formally in a mathematical appendix. The available structural data are explained, including the fd DNA pitch indicated by x-ray diffraction photos and the similar DNA morphologies of Xf and fd. Predictions are made for the existence of nonclassical inverted DNA structures (I-DNA) in Pf1 and Pf3.
mesh_terms: D001435:Bacteriophages / Q000648:ultrastructure*; D003090:Coliphages / Q000648:ultrastructure*; D004279:DNA, Viral / Q000502:physiology*; D008433:Mathematics; D008954:Models, Biological; D009690:Nucleic Acid Conformation; D011487:Protein Conformation; D013045:Species Specificity; D014764:Viral Proteins / Q000502:physiology*
chemical_list: D004279:DNA, Viral; D014764:Viral Proteins