Reversible block in intracellular transport and budding of mutant vesicular stomatitis virus glycoproteins

The blocks in intracellular maturation of glycoprotein (G protein) synthesized by two temperature-sensitive vesicular stomatite's virus (VSV) mutants are reversible. Our earlier work demonstrated that at 40 degrees, the nonpermissive temperature, mutant ts L513(V) G protein accumulates in the rough endoplasmic reticulum. Here we show that when the temperature is lowered the high-mannose oligosaccharides on a significant fraction of ts L513(V) G protein, synthesized at 40 degrees, will be modified to the complex type. Moreover, when the temperature is lowered ts L513(V) G protein accumulated at 40 degrees will mature to the cell surface, as evidenced by its accessibility to extracellular trinitrobenzene sulfonate, and into virions. G protein synthesized at 40 degrees in ts L511(V)-infected cells undergoes most of the processing events characteristic of the Golgi complex. Although we reported previously that no ts L511(V) G protein reaches the plasma membrane at 40 degrees, we now find, using more sensitive techniques, that an appreciable fraction does reach the cell surface. ts L511(V) G protein is lost from the cells but is not incorporated into virions. However, an appreciable fraction of the ts L511(V) G protein which accumulates in cells at 40 degrees will mature into virions when the temperature is lowered. These results exclude irreversible denaturation of mutant G proteins as a cause of the block in intracellular maturation and virus budding.