Studies on the arrangement patterns of nucleocapsids within the envelopes of nuclear-polyhedrosis virus in the fat-body cells of the brown tail moth, Euproctis similis

Electron microscopical studies were made of the arrangement patterns of nucleocapsids within the envelope of the nuclear-polyhedrosis virus with naturally infected larvae of the brown tail moth, Euproctis similis. Number of nucleocapsids observed in an envelope in their cross sections ranged from 1 to 39, and the frequencies at 4, 7, 10, 12, 14, 16, 19, 21, and 24 nucleocapsids were significantly higher than the others, suggesting that these numbers of nucleocapsids were more commonly involved in an envelope. Arrangement patterns represented by these particular numbers of nucleocapsids seemed to be regulated by some unknown mechanisms. However, it was speculated that polygonal shapes such as triangle, lozenge, trapezium, pentagon, or hexagon of cross-sectioned envelopes would have resulted from a well-regulated mode of assemblage of the component nucleocapsids as described. More than three nucleocapsids are more stable when they are made into a bundle, in which lateral surfaces of the nucleocapsids are circumscribing each other and fitting in at angles of about 60° as depicted in Figure 24. The central row is always composed of the largest number of nucleocapsids and two rows consisting of the one less number of nucleocapsids are disposed on the both sides of the central row, thenceforth a certain number of rows involving nucleocapsids that decrease by one in due order being situated bilaterally, finally forming the polygonal-shaped outline. Therefore, the total number of nucleocapsids increases in proportion to the numbers of nucleocapsids in the central row and to the numbers of rows.