EVIDENCE FOR VIRUS-ENCODED GLYCOSYLATION SPECIFICITY

Four spontaneously derived serologically distinct classes of mutants o f the Paramecium bursaria chlorella virus (PBCV-1) were isolated using polyclonal antiserum prepared against either intact PBCV-1 or PBCV-1- derived serotypes. The oligosaccharide(s) of the viral major capsid pr otein and two minor glycoproteins determined virus serological specifi city. Normally, viral glycoproteins arise from host-specific glycosyla tion of viral proteins; the glycan portion can be altered only by grow ing the virus on another host or by mutations in glycosylation sites o f the viral protein. Neither mechanism explains the changes in the gly can(s) of the PBCV-1 major capsid protein because all of the viruses w ere grown in the same host alga and the predicted amino acid sequence of the major capsid protein was identical in the PBCV-1 serotypes. PBC V-1 antiserum resistance is best explained by viral mutations that blo ck specific steps in glycosylation, possibly by inactivating glycosylt ransferases.