Sequences of the gene encoding the PP3 protein of sigma virus that contain clusters of A to G mutations. The sequences are shown in positive sense (the mRNA sequence rather than the genome sequence). (a) Isolates A3 and A3 E55 (2'916 - 2'316). These were laboratory maintained lines that were split from each other ~15 years ago. (b) The field isolate DM113 (3'194 - 2'954). (c) The field isolate U125 (2'693 - 2'574). (d) The field isolate Derby (3'074 - 2'954). This isolate was polymorphic for five A to G changes in the PP3 protein (these ambiguous bases are indicated by the wobble code R). In all the panels, sites that have not been mutated are represented by a period and the ancestral sequences were reconstructed by parsimony using a phylogeny of the viral sequences. The nucleotide locations refer to the position in negative sense genome of Genbank accession AM689308 (isolate A3).