Chlorella virus PBCV-1 particles contain three glycoproteins, the major capsid protein Vp54 and two minor proteins Vp280 and Vp260. The major capsid protein is myristylated as well as glycosylated. Both modifications are in the carboxyl-terminal portion of the protein. A gene which is modified in a PBCV-1 antiserum-resistant mutant was cloned and sequenced. This gene has an open reading frame of 3099 bases and encodes one of the two large virion glycoproteins (Vp260). Vp260 contains 13 tandem repeats of 61 to 65 amino acids. The mutation deletes the equivalent of four of the amino acid repeat sequences and duplicates one of these sequences.