The brown algal virus EsV-1 particle contains a putative hybrid histidine kinase

The Ectocarpus sillculosus virus, EsV-1, occurs worldwide in all population s of the filamentous marine brown alga E. siliculosus. We have screened an expression library of EsV-1 restriction fragments and identified a DNA clon e with the potential to code for a 52-kDa histidine protein kinase. The der ived amino acid sequence includes all homology boxes diagnostic for histidi ne protein kinases and, in addition, amino acid motifs that are commonly fo und in response regulators of bacterial two-component signal transduction p roteins. Thus, the novel viral protein can be classified as a hybrid histid ine protein kinase of a type that has previously been detected in fungi, sl ime molds, and plants. By using purified antibodies, we found that the prot ein with its potential kinase activity is located on the outer shell of vir al particles. This is the first report on a two-component regulator-like pr otein in viruses and could provide the basis for speculations with regard t o the evolution of EsV-1 and related viruses. (C) 2000 Academic Press.