Morphogenesis of the wild-type PRV Fa strain. Formation of capsids in the PK15 cell nucleus and a large number of nucleocapsids aggregated and arrayed as pseudocrystals were observed under 25,000 × amplification (A). The gap in the nuclear membrane was distended and a nucleocapsid was budding through the inner nuclear membrane to acquire a primary envelope indicated by the arrow (B, 30,000×). Virions in the envelope and numerous nucleocapsids scattered in the nucleus were observed (C, 25,000×). Fusion of a primary envelope with the outer nuclear membrane, and nucleocapsids released into the cytoplasm, and loss of a primary envelope; the arrow points to a budding process (D, 20,000×). A secondary envelope was acquired in the trans-Golgi area of the perinuclear cisterna (E, 25,000×). Newly produced viral progeny was released to the cell surface through the fusion of a transport vesicle and the cytoplasmic membrane via exocytosis (F, 30,000×).