Study of negatively stained images of Sendai virus nucleocapsids using minimum-dose system

Using minimum-dose system and optical diffraction, effects of electron irradiation on negatively stained images of trypsin-straightened nucleocapsids of Sendai virus were semiquantitatively compared for uranyl-acetate (UA) and phosphotungstic acid (PTA). The results confirmed the superiority of UA in display of fine structures and showed that both UA- and PTA-stained images tended to turn from a one-sided to a two-sided image during irradiation, the general contrast of the picture increased in the UA-stained images but not in the PTA-stained ones, and furthermore the electron doses for the richest information were 18 000 to 30 000 e-/nm2 for UA, but 1000 e-/nm2 for PTA, under the condition used. The optical diffraction patterns of the UA-stained nucleocapsids, its analysis by the superposition method, and rotational harmonics of end-on views of nucleocapsids, together indicated that the most probable arrangement of subunits was 13 per turn of a helix with 5-nm periodicity. This helix also had an arrangement of subunits parallel to the axis. The occurrence of 2.5 nm periodicity was probably produced by an arrangement of a UA-penetrable concave substructure of the subunit.