CHARACTERIZATION OF EARLY STAGES IN VACCINIA VIRUS MEMBRANE BIOGENESIS - IMPLICATIONS OF THE 21-KILODALTON PROTEIN AND A NEWLY IDENTIFIED 15-KILODALTON ENVELOPE PROTEIN

Vaccinia virus (VV) membrane biogenesis is a poorly understood process . It has been proposed that cellular membranes derived from the endopl asmic reticulum-Golgi intermediate compartment (ERGIC) are incorporate d in the early stages of virion assembly. We have recently shown that the VV 21-kDa (A17L gene) envelope protein is essential for the format ion of viral membranes. In the present work, we identify a 15-kDa VV m embrane protein encoded by the A14L gene. This protein is phosphorylat ed and myristylated during infection and is incorporated into the viri on envelope. Both the 21- and 15-kDa proteins are found associated wit h cellular tubulovesicular elements related to the ERGIC, suggesting t hat these proteins are transported in these membranes to the nascent v iral factories. When synthesis of the 21-kDa protein is repressed, org anized membranes are not formed but numerous ERGIC-derived tubulovesic ular structures containing the 15-kDa protein accumulate in the bounda ries of the precursors of the viral factories. These data suggest that the 21-kDa protein is involved in organizing the recruited viral memb ranes, while the 15-kDa protein appears to be one of the viral element s participating in the membrane recruitment process from the ERGIC, to initiate virus formation.