A Pre-Golgi Copartment Connecting Golgi Cisterns to the Perinuclear Space in Bovine Herpesvirus 1 (Bhv-1) Infected Mdbk Cells. Evidence for an Intracisternal Pathway

The nucleocapsid of herpesviruses is assembled within the nucleus and transported to the perinuclear space by budding through the inner nuclear membrane. The route from the perinuclear space to the plasma membrane for exocytotic release is assumed to involve loss of the acquired envelope by fusion with the outer nuclear membrane followed by wrapping of the nucleocapsid by Golgi membranes. Alternatively, virions are thought to leave the perinuclear space via vacuoles originating from the outer nuclear membrane. Non of these processes has been shown so far. We thus examined the nuclear periphery of MDBK cells infected with BHV-1 by cryobased electron microscopy. Infected cells were high-pressure frozen at 4, 5 and 6 hours of incubation, and freezesubstituted employing a protocol yielding high resolution of membranes.Thin sections stained with uranyl acetate and lead citrate showed 3 distinct stages of viral envelopment at any time of incubation.