The large chlorella virus PBCV-1, which contains double-stranded DNA (dsDNA), encodes a 94-codon open reading frame (ORF) that contains a motif resembling the signature sequence of the pore domain of potassium channel proteins. Phylogenetic analyses of the encoded protein, Kcv, indicate a previously unidentified type of potassium channel. The messenger RNA encoded by the ORF leads to functional expression of a potassium-selective conductance in Xenopus laevis oocytes. The channel blockers amantadine and barium, but not cesium, inhibit this conductance, in addition to virus plaque formation. Thus, PBCV-1 encodes the first known viral protein that functions as a potassium-selective channel and is essential in the virus life cycle.

We have started to characterize the capsid components of European Chlorella virus isolate CVG-1, a member of the Pbi subgroup of the Phycodnaviridae. The major coat protein, Vp49, was biochemically characterized and the amino acid sequence of the N terminus was determined. Subsequently, the corresponding gene was isolated from CVG-1 genomic DNA. Sequence data were compared to those available from PBCV-1 and other Chlorella virus isolates representing the NC64A subgroup of the Phycodnaviridae. The major coat proteins of all strains are homologous and similar in size, but apparently differ in their degree of glycosylation. Like PBCV-1, the major coat protein of CVG-1 is part of a gene family, as two open reading frames with high similarity to Vp49 were also isolated and characterized in this study. The predicted amino acid sequences of the CVG-1 and PBCV-1 virus genes examined show, with one exception, a divergence of about 25 %. Taking into account that corresponding genes of NC64A viruses are almost identical, this divergence supports the original placement of the NC64A and Pbi viruses into separate subgroups of the Phycodnaviridae.