ENCAPSIDATED CONFORMATION OF BACTERIOPHAGE-T7 DNA

The structural organization of encapsidated T7 DNA was investigated by cryo-electron microscopy and image processing. A tail-deletion mutant was found to present two preferred views of phage heads: views along the axis through the capsid vertex where the connector protein resides and via which DNA is packaged; and side views perpendicular to this a xis. The resulting images reveal striking patterns of concentric rings in axial views, and punctate arrays in side views. As corroborated by computer modeling, these data establish that the T7 chromosome is spo oled around this axis in approximately six coaxial shells in a quasicr ystalline packing, possibly guided by the core complex on the inner su rface of the connector.