Tunicamycin inhibits glycosylation of precursor polyprotein encoded by env gene of Rauscher murine leukemia virus.

The molecular weight of the precursor polyprotein to the envelope proteins of Rauscher murine leukemia virus is reduced from 85,000 to 68,000 daltons when synthesized in the presence of tunicamycin, a specific inhibitor of the synthesis of oligosaccharides that attach to glycoproteins via asparagine residues. The unglycosylated precursor protein (Pr68^$\text{env}$) is synthesized at a rate comparable to that of the normal carbohydrate-containing envelope precursor (gPr85^$\text{env}$). Pr68^$\text{env}$ is not proteolytically processed and remains undegraded in the cell. Thus, most if not all of the carbohydrate content of gPr85^$\text{env}$ is N-linked, and glycosylation appears to be necessary for normal processing of precursor proteins into viral particles.