Fig. 1.

a Nucleotide sequences of the inferred pxr ancestor and extant homologs at every site from 5′ to 3′. A dot indicates a nucleotide identical to the corresponding site for the inferred ancestor at the internal node shared by the non-Stigmatella homologs, whereas letters show nucleotide differences. The cladogram of the pxr homologs is shown on the left. The consensus stem-loops based on the single-copy homologs are annotated as SL1, SL2 and SL3 at the bottom. Brackets represent nucleotides positioned on the stems. b The predicted secondary structure of the Pxr ancestor, which has a calculated self-folding free energy of −57.5 kcal/mol. The nucleotide numbers correspond to the alignment positions in (a). c Genetic organization of pxr alleles and their neighboring genes in different myxobacterial species. Gene and intergenic region lengths are not drawn to scale