A MODEL OF THE BINDING, ENTRY, UNCOATING, AND RNA-SYNTHESIS OF SEMLIKI-FOREST-VIRUS IN BABY HAMSTER-KIDNEY (BHK-21) CELLS

A quantitative understanding of viral trafficking would be useful in t reating viral-mediated diseases, designing protocols for viral gene th erapy, and optimizing heterologous protein production. In this article , a model for the trafficking of Semliki Forest virus and its RNA synt hesis in baby hamster kidney (BHK-21) cells is presented. This model i ncludes the various steps leading to infection such as attachment, end ocytosis, and viral fusion in the endosome. The model estimates a mean fusion time of 4 to 6 min for the wild-type virus, and 38 min for Fus -1, an SFV mutant which requires a lower pH for fusion. These mean fus ion times are consistent with the time-scale of endosomal acidificatio n, suggesting viruses fuse almost instantaneously with the endosomal m embrane as soon as the pH of the endosome drops below the pH threshold of the virus. Infection is most likely controlled at the level of vir al uncoating, as shown by the close agreement between the efficiency o f uncoating and the experimentally determined fraction of viruses that is infectious. The viral RNA synthesized per cell is best described b y assuming that it depends on the number of uncoated viruses prior to the onset of replication according to a saturation-type expression. A Poisson distribution is used to determine the distribution of uncoated viruses among the cells. Because attachment is the rate-limiting step in the uncoating of the virus, increasing the attachment rate can lea d to enhanced RNA synthesis and, hence, new virion production. Such an increase in the attachment rate may be obtained by lowering the mediu m pH or the addition of a polycation. (C) 1995 John Wiley & Sons, Inc.