Evidence for a frame-shift mutation within the M135R gene from Danish samples of myxoma virus. Panel (a). The nucleotide sequence of the myxoma virus M135R gene, plus flanking sequences, is shown. Primers M135Rfor and M135Rrev (see Table 2), indicated in bold italics, were used to amplify by PCR the M135R gene, together with some flanking sequences at both termini, and these fragments were sequenced directly. The myxoma virus sequences included in primers M135RXFOR and M135RAPAREV (Table 2) for amplifying the coding sequence for M135R are underlined. The initiation and termination codons within these primers are indicated in bold capitals. The region of the gene in which a frame-shift mutation was present in certain virus samples is indicated within a rectangle. Panels (b) and (c.) Sequence traces obtained by analysis of a wt M135R gene sequence (as in the myxoma vaccine, panel (b)) and the mutant (+G) form (panel (c)) found in the majority of Danish clinical samples in 2007. The region shown corresponds to the portion of the sequence contained within the rectangle in panel (a). The region of the M135R gene which is predicted to be translated in a different reading frame, downstream of the insertion of a G nucleotide, is indicated in red in panel (a). The termination codons (TAA) for the wt and mutant M135R gene products are indicated in bold capitals.