Table 1.

Average values of DNA–DNA d-spacings between the DNA layers and the interaxial spacings for phage λ DNA length mutants with and without spermine added

	d-spacings (in Å)	Interaxial spacings (in Å)
100% WT phage λ (48.5 kb)	22.7	26.2
100% WT phage λ (48.5 kb) + 1.3 mM spermine	22.7	26.2
94% DNA phage λ (46.5 kb)	24.6	28.4
78% DNA phage λ (37.8 kb)	25.7	29.7
78% DNA phage λ (37.8 kb) + 1.3 mM spermine	25.2	29.1
30% DNA phage λ in LamB + 1.3 mM spermine	27.6	31.9
Bulk DNA condensed by 1.3 mM spermine in TM buffer solution	25.2	29.1

DNA d-spacings were determined from 3D reconstructions performed using 5000 particles for each phage mutant to maintain consistency between the data. Using higher numbers of particles did not change the d-spacing values. Based on the pixel size and the Gaussian spread of the radially averaged rings of DNA density, we calculate the centre of the density of each individual DNA ring to within ∼0.4 Å (standard error). We also show d-spacing and interaxial spacing values for bulk DNA condensed by 1.3 mM spermine in TM buffer solution, measured by X-ray diffraction (13).