Heterologous expression of the membrane proteins that control cellular excitability.

Versatile and potent expression systems are needed to decipher the structure and functions of the many excitability proteins that have been identified through molecular cloning. This article reviews the use of recombinant vaccinia viruses (VV), which have been recently explored for the heterologous expression of eukaryotic proteins. Vaccinia viruses feature a series of favourable properties, most of all a broad host range and high efficiency of infection, that make them uniquely suited as flexible expression vectors. In one type of experiment, the recombinant virus simply harbors the cDNA for the foreign protein; in a second type the virus harbors the cDNA for the specific and efficient RNA polymerase of bacteriophage T7, which in turn generates RNA from a separate introduced plasmid or virus. Both variations have been successfully applied to the expression and analysis of voltage-dependent ion channels, neurotransmitter receptors and other excitability proteins in many cell lines and postmitotic cells in culture. VV vectors promise to be particularly useful to study membrane proteins that require posttranslational processing, association with cell-specific subunits or coupling to endogenous second messengers pathways.