title: DNA structure: evidence from electron microscopy.
abstract: The contour lengths of phiX174 DNA duplex and RNA-DNA hybrid molecules were measured by several commonly used electron microscopic techniques. The countour length of the hybrid molecules corresponds to a rise of 2.5 to 2.6 angstroms per base pair, as expected for the A conformation, while the length of phiX174 duplex DNA similarly measured corresponds to a 2.9-angstrom rise, very different from 3.4 angstroms of the classic B form. Thus any chromatin structure parameter based on electron microscopy and a rise of 3.4 angstroms must be reappraised. The possibility that DNA in dilute solution also has a rise of 2.9 angstroms and a screw of 10.5 base pairs per turn is discussed.
mesh_terms: D003090:Coliphages / Q000648:ultrastructure; D004270:DNA, Circular; D004279:DNA, Viral; D008854:Microscopy, Electron / Q000379:methods; D009690:Nucleic Acid Conformation; D009693:Nucleic Acid Hybridization
chemical_list: D004270:DNA, Circular; D004279:DNA, Viral