Fig. 3.

Bayesian relaxed molecular clock of Type I reaction centres. The tree was calculated assuming that Type I reaction centres had originated by 3.5 Ga (grey dot). The orange dot indicates the duplication event that allowed the divergence of PsaA and PsaB. Red dots highlight the nodes that were calibrated as described in Materials and Methods. The light grey bars along the nodes show the uncertainty, 95% confidence interval, on the estimated divergence time. Sequences marked as hA denote those from strains of Heliobacteria, while those marked as cA from Chlorobi and Acidobacteria. Sequences marked as A and B represent PsaA and PsaB from Cyanobacterial and eukaryotic PSI. The blue bar marks the GOE.