Expression of genes coding for animal virus glycoproteins in heterologous systems

The outermost layers of animal viruses are usually composed of glycoprotein s. They are responsible not only for the entrance of viruses into, and rele ase from host cells but also for the initial interaction of a viral particl e with immunological defense of the host. It is therefore not surprising th at many laboratories devote a lot of effort to study viral glycoproteins at the molecular level. Very often such studies are possible only after the i ntroduction of a glycoprotein gene into a heterologous system. Expression o f glycoprotein genes is usually obtained in mammalian or insect cells. Expr ession in mammalian cells yields viral glycoproteins with glycan chains ind istinguishable from the original counterparts in virion particles but the l evel of synthesis of glycoproteins is very low. Vaccinia virus is the most common vector for expression in mammalian cells. It is easy to grow, the in troduction of foreign genes is relatively simple and, due to the size of th e vaccinia genome, it can accept large pieces of foreign DNA. Glycosylation in insect cells is not as complex as in mammalian cells and usually glycop roteins produced in insect cells are of slightly lower molecular mass than those produced in mammalian cells. The most common vector for expression of glycoproteins in insect cells is a baculovirus, Autographa californica nuc lear polyhedrosis virus (AcNPV). The great advantage of this system is a ve ry high level of expression of foreign genes.