A Low Resolution Model of the Substructure of the Capsids of Immunodeficiency Viruses
The capsids of the primate immunodeficiency viruses (PIV) SIV, HIV-1, and HIV-2 are visualized in traditional electron microscopic images as a bullet-shaped core with no discernible substructure. In this study, computer assisted image processing, i.e., two-dimensional fast Fourier transform (2D-FFT) filtering, has been used to reveal a previously undescribed substructure in the capsids of mature HIV types 1 and 2 and SIV. Transmission electron micrographs of thin-sectioned, resin-embedded PIV were processed using 2D-FFT filtering to attenuate the low resolution and amplify the high resolution components of the images. The resultant images revealed five rotationally symmetric subunits in the capsids. Application of 2D-FFT filtering to longitudinal sections of PIV revealed the subunits to be rodlike structures that rise at an angle of 60° relative to the base of the capsid. Three-dimensional reconstruction from a series of cross-sectional images demonstrated the PIV capsid consists of these subunits arranged in a right-handed helical bundle of five subunits that form a cage which presumably carries the viral RNA, nucleocapsid proteins, and reverse transcriptase in mature PIV.
Maleeff, BE; Hart, TK; Smith, WW; Bugelski, PJ
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