Protein composition of wild-type, gp17-minus, gp50-minus and gp65-minus virions. Arrows denote proteins absent in virions lacking gp50, gp65, or gp17. For properties of gene products, refer to Table 1.

Structure of gp65-minus mutant virus. (a) Surface representation of the asymmetric reconstruction of gp65-minus mutant virus showing a side view (left) and an end-on view looking down the long axis of the phage (right). The color scheme is the same as in Figure 3. One icosahedral asymmetric unit is outlined in black. The scale bar represents 300 Å. (b) Central cross-section of the asymmetric reconstruction of gp65-minus virus. (c) Tilted view of the tail for the 6-fold-averaged gp65-minus virus (left) and an end-on view (right). (d) Difference map calculated between asymmetric reconstructions of wild-type and gp65-minus viruses showing the non-contractile tail sheath (gp65).

Structures of the mature and gp17-minus N4 head. (a) Surface rendering of the N4 head viewed down an icosahedral 2-fold axis (top). The density is contoured at 3σ. The asymmetric unit is outlined by a black triangle connecting 5-, 3-, and 2-fold symmetry axes. One pentamer at the icosahedral 5-fold axis, one hexamer in a general position, and two hexamers at the icosahedral 3-fold axes are colored in orange, green, and purple, respectively. The scale bar represents 300 Å. Two independent hexamers and the pentamer in the gp17-minus virus are enlarged in order to show their similarities (bottom). (b) Central cross-section of the N4 head reconstruction. Density connecting the capsid to the most external DNA layer is indicated by a red arrow. The orthogonal icosahedral 2-fold axes are indicated with white arrows. (c) A schematic diagram of the T = 9 icosahedral lattice. The T = 9 hexagonal lattice and the icosahedral asymmetric unit are shown. The positions of nine major capsid protein subunits in an icosahedral asymmetric unit are labeled as 1-9. Subunit 1 forms one fifth of a pentamer (orange), subunit 2-7 form a general hexamer (green), each of subunit 8 and 9 form one sixth of a hexamer at the icosahedral 3-fold axis (purple). (d) Difference density between the wild-type and gp17-minus viruses. For clarity, only the front half of the map is shown. A T = 9 icosahedral lattice and asymmetric unit are shown. The three molecules of gp17 per icosahedral asymmetric unit are labeled A, B, and C. (e) The difference density between the wild-type and gp17-minus (green) superimposed with gp17-minus virus (blue to white with increasing radius). (f) Stereo view showing the fit of IgG domains into the difference density at two different contour levels. The grey caged density represents 3 σ, and a green solid density represent 5 σ above mean The three IgG domains (Protein Data Bank accession number 1FNH) were fitted as two separate rigid bodies (DI-II in magenta and DIII in blue). Three gp17 molecules are labeled as in (d). A symmetric unit (top) and a side view of the molecule B and C (bottom) are shown.

Structure of the mature N4 phage. (a) Surface representation of the asymmetric reconstruction of the mature N4 phage showing a side view (left) and an end-on view looking down the long axis of the phage (right). The head is colored from blue to white with increasing radius. The appendages (gp66), neck, non-contractile sheath (gp65), and tail tube are colored in orange, brown, green, and yellow, respectively. One icosahedral asymmetric unit is outlined in black. The scale bar represents 300 Å. (b) Central cross-section of the asymmetric reconstruction of the N4 phage. The distal domain of the appendages is marked with a star. (c) Enlarged tilted (left) view, end-on view (middle), and central section (right) of the 6-fold-averaged tail.

The interior of bacteriophage N4. (a) The N4 portal assembly showing the crown, wing and the stalk domains. The atomic structure of the ϕ29 connector protein (Protein Data Bank accession number 1H5W) was fitted into the 5-fold-averaged cryoEM density of the N4 portal assembly. The α-helices and β-strands of the ϕ29 connector are shown in red and purple, respectively. (b) Comparison of wild-type and gp50-minus viruses. Cross section of the 5-fold-averaged wild-type (left) and gp50-minus (right) viruses viewed perpendicular to the long axis of the phage. The densities are displayed at 2.5σ above their respective means to show the molecular boundaries of portal and inner core proteins. The dsDNA, inner core proteins, and portal assembly are colored in dark green, orange, and red, respectively. All the other components of the phage are colored as in Figure 3.