Intracellular trafficking of the UL11 tegument protein of herpes simplex virus type 1

Growing evidence indicates that herpes simplex virus type I (HSV-1) acquire s its final envelope in the trans-Golgi network (TGN). During the envelopme nt process, the viral nucleocapsid as well as the envelope and tegument pro teins must arrive at this site in order to be incorporated into assembling virions. To gain a better understanding of how these proteins associate wit h cellular membranes and target to the correct compartment, we have been st udying the intracellular trafficking properties of the small tegument prote in encoded by the U(L)11 gene of HSV-1. This 96-amino-acid, myristylated pr otein accumulates on the cytoplasmic face of internal membranes, where it i s thought to play a role in nucleocapsid envelopment and egress. When expre ssed in the absence of other HSV-1 proteins, the UL11 protein localizes to the Golgi apparatus, and previous deletion analyses have revealed that the membrane-trafficking information is contained within the first 49 amino aci ds. The goal of this study was to map the functional domains required for p roper Golgi membrane localization. In addition to N-terminal myristylation, which allows for weak membrane binding, UL11 appears to be palmitylated on one or more of three consecutive N-terminal cysteines. Using membrane-pell eting experiments and confocal microscopy, we show that palmitylation of UL 11 is required for both Golgi targeting specificity and strong membrane bin ding. Furthermore, we found that a conserved acidic cluster within the firs t half of UL11 is required for the recycling of this tegument protein from the plasma membrane to the Golgi apparatus. Taken together, our results dem onstrate that UL11 has highly dynamic membrane-trafficking properties, whic h suggests that it may play multiple roles on the plasma membrane as well a s on the nuclear and TGN membranes.