Coat protein of the Ectocarpus siliculosus virus

Ectocarpus siliculosus virus, EsV, multiplies in sporangia and gametangia of the marine brown alga Ectocarpus siliculosus. We describe an improved method for the isolation of morphologically intact and infectious virus from diseased plants. We show that treatment of virus particles with high concentrations of CsCl results in a substantial loss of structural proteins. One of the proteins which resists CsCl treatment is glycoprotein-1, the largest of the three viral glycoproteins. We have isolated an EsV genomic fragment with an open reading frame encoding glycoprotein-1. The predicted amino acid sequence is rich in hydrophilic amino acids, but contains hydrophobic regions close to the amino and carboxy termini. A discrepancy between the molecular weight predicted from the coding region and the molecular weight determined by gel electrophoresis suggests that proteolytic processing is required for the maturation of the protein.