Some of the transported proteins contain information, which target them to their correct intracellular locations. Enveloped viruses have been useful tools for almost three decades to study the mechanisms of protein transport and sorting along the exocytic pathway. The simple structure of viruses force them to rely on host cell mechanisms. This includes the synthesis, processing, modification and transport o their membrane proteins. Enveloped viruses acquire their lipoprotein coat by budding through one of the cellular membranes.
Some viruses bud at the plasma membrane whereas others mature at intracellular membranes.
The site of budding is thought to be determined by the accumulation of viral membrane glycoproteins in the budding compartment. Such viral glycoproteins are likely to contain signals that retain them in the budding compartment. As a model system to study retention of proteins in the GC, we are using the viral heterodimeric spike glycoproteins G1 and G2 of Uukuniemi virus, a phlebovirus within the Bunyaviridae family. We present evidence that the signal sequence of G2 remains attached to the C-terminus of G1. The glycoproteins are inserted in the membrane as type I membrane proteins with their C-terminal tails exposed in the cytoplasm.