Phylogenetic tree of Fv1 sequences.
The tree was generated from the open reading frames listed in Tables 1 and 2 (bases 1 to 1278 in Fv1b) using the MegAlign programme from the DNASTAR Lasergene package. The highly divergent C-terminus was excluded from the analysis and the aspartic acid residue at position 426 (Fv1b numbering), which was the last residue conserved in all the sequences, was chosen as the cut-off point. The number of substitution events is shown at the bottom of the tree while the distances between sequence pairs is represented by the length of the branch pairs. The distance values were calculated using the Kimura distance formula that takes into account the number of non-gap mismatches and silent substitutions.