Figure 1. Maximum likelihood tree based on partial nonstructural (NS5) protein sequence data (see text) with the third codon position and the hypervariable loop excluded. Sequences were assumed to evolve according to the HKY85 substitution model with the rate of transitions and transversions and the extent of among- site variation in substitution rate ( distribution – which allows for the distribution of substitution rates) estimated from the data. Sof is a strain of FETBE virus. This tree was constructed and kindly supplied by Dr Edward Holmes, Department of Biology, The Pennsylvania State University, Mueller Laboratory, University Park, PA 16802, USA.