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On the structure of the cytoplasmic-polyhedrosis virus of the silkworm, Bombyx mori
JOURN.4L
OF
O n the
INVERTEBRATE
Structure
PATHOLOQY
19, tti%280
of the Cytoplasmic-Polyhedrosis Silkworm, Bombyx mori
It is generally accepted that the cytoplasmic-polyhedrosis virus (CPV) particle is an icosahedron with a projection at each vertex (Y. Hosaka and K. Aizawa, J. Insect Pathol. 6, 53-77, 1964). Hemagglutination (HA) of CPV with vertebrate red blood cells suggested that the projection might be an active site of CPV adsorption onto the host cell or red blood cell (S. Miyajima and S. Kawase, vi&ogzl 39, 347-348, 1969). The present paper is concerned with the fine structure of these projections as revealed by the electron microscope. Virus particles were isolated from partially purified polyhedra by treatment with alkali (0.1 x Na2COa-NaHCOs, pH 10.8) according to the mod&d method of T. Hukuhara and Y. Hashimoto (J. Invert&r. Pdhol. 8, 236 239, 1966). The freshly prepared samples were stained with a 1 % solution of potassium phosphotungstate adjusted to pH 7.4, and examined in a Hitachi HU-11-D electron microscope. Figure 1 illustrates the CPV particles. Spherical particles indicated by arrows exist on the top of some projections. They are homogeneous in size and shape (12 f 1 nm in diameter) and attach only to the projections. Some isolated particles are seen in Figs. 2B-D. CPV particles stained with 1 % uranyl acetate (pH 4.5) or 2 % ammonium molybdate (pH 7.4) also had the same structure. Also, nonoccluded virions, isolated by the method of Y. Hayashi and F. T. Bird
Copyright
Q 1978 by
(1972)
Academic Press, Inc.
Virus
of the
(Can. J. Microbial. 16, 695-701, 1970), appeared to be very similar to those that had been occluded. The particle may be concerned with adsorption of CPV to the host cell and/or hemagglutination of red blood cell as in other hemagglutinating viruses, i.e., adenovirus, myxovirus, etc. In a previous paper (S. Miyajima and S. Kawase, 1969) the HA4 activity of CPV gradually decreased when kept at 4°C for more than 2 days, and little or no HA activity sometimes occurred in the course of virus purification. These data indicat,e that the particles may have been lost from the virus under these conditions. If so, it is conceivable that the HA activity is closely related to these, newly observed, spherical particles. W e thank Prof. K. Hasegawa, Faculty of Agriculture, Nagoya University, for advice and encouragement during the course of this work. W e are also grateful for Drs. H. Nagura and Y. Itatsu, Nagoya University School of Medicine, for their kind suggestions. JUNPEI
i&AI’
FUMIMKO SHIQEMI
KAWAMOTO~ KAWASE~
Received September 4, 1971 1 Department of Pathology, Nagoya University School of Medicine, Shows-ku, Nagoya; ZFaculty of Agriculture, Nagoya University, Chikusa-ku, Nagoya,
279
Japan
FIG. 1. Electron
micrograph of negatively stained CPV showing the spherical particles indicated by at the top of the projections. FIG. ZA-D. Electron micrographs showing projections and spherical particles of CPV. A, spherical particles attaching at the top of projections; B-D, spherical particles detached from projections. arrows
OF
O n the
INVERTEBRATE
Structure
PATHOLOQY
19, tti%280
of the Cytoplasmic-Polyhedrosis Silkworm, Bombyx mori
It is generally accepted that the cytoplasmic-polyhedrosis virus (CPV) particle is an icosahedron with a projection at each vertex (Y. Hosaka and K. Aizawa, J. Insect Pathol. 6, 53-77, 1964). Hemagglutination (HA) of CPV with vertebrate red blood cells suggested that the projection might be an active site of CPV adsorption onto the host cell or red blood cell (S. Miyajima and S. Kawase, vi&ogzl 39, 347-348, 1969). The present paper is concerned with the fine structure of these projections as revealed by the electron microscope. Virus particles were isolated from partially purified polyhedra by treatment with alkali (0.1 x Na2COa-NaHCOs, pH 10.8) according to the mod&d method of T. Hukuhara and Y. Hashimoto (J. Invert&r. Pdhol. 8, 236 239, 1966). The freshly prepared samples were stained with a 1 % solution of potassium phosphotungstate adjusted to pH 7.4, and examined in a Hitachi HU-11-D electron microscope. Figure 1 illustrates the CPV particles. Spherical particles indicated by arrows exist on the top of some projections. They are homogeneous in size and shape (12 f 1 nm in diameter) and attach only to the projections. Some isolated particles are seen in Figs. 2B-D. CPV particles stained with 1 % uranyl acetate (pH 4.5) or 2 % ammonium molybdate (pH 7.4) also had the same structure. Also, nonoccluded virions, isolated by the method of Y. Hayashi and F. T. Bird
Copyright
Q 1978 by
(1972)
Academic Press, Inc.
Virus
of the
(Can. J. Microbial. 16, 695-701, 1970), appeared to be very similar to those that had been occluded. The particle may be concerned with adsorption of CPV to the host cell and/or hemagglutination of red blood cell as in other hemagglutinating viruses, i.e., adenovirus, myxovirus, etc. In a previous paper (S. Miyajima and S. Kawase, 1969) the HA4 activity of CPV gradually decreased when kept at 4°C for more than 2 days, and little or no HA activity sometimes occurred in the course of virus purification. These data indicat,e that the particles may have been lost from the virus under these conditions. If so, it is conceivable that the HA activity is closely related to these, newly observed, spherical particles. W e thank Prof. K. Hasegawa, Faculty of Agriculture, Nagoya University, for advice and encouragement during the course of this work. W e are also grateful for Drs. H. Nagura and Y. Itatsu, Nagoya University School of Medicine, for their kind suggestions. JUNPEI
i&AI’
FUMIMKO SHIQEMI
KAWAMOTO~ KAWASE~
Received September 4, 1971 1 Department of Pathology, Nagoya University School of Medicine, Shows-ku, Nagoya; ZFaculty of Agriculture, Nagoya University, Chikusa-ku, Nagoya,
279
Japan
FIG. 1. Electron
micrograph of negatively stained CPV showing the spherical particles indicated by at the top of the projections. FIG. ZA-D. Electron micrographs showing projections and spherical particles of CPV. A, spherical particles attaching at the top of projections; B-D, spherical particles detached from projections. arrows