su(w^a)^suRS is identical to wild type su(w^a) from the promoter region through to the codon encoding amino acid 963. It also carries the 3'-untranslated region and polyadenylation signal from the tra gene (corresponding to 957bp through to approximately 1260bp in the wild-type tra sequence) in place of the su(w^a) 3'-untranslated segment (the segment from 5362bp through to 5857bp of the wild-type su(w^a) is replaced).