Origin of GPCRs Figure 2. Phylogenetic relationships between the cAMP and Rhodopsin families across eukaryotic lineages. The tree is based on Bayesian method of phylogenetic inference. The phylogenetic tree is based only on the transmembrane region. Robustness of the nodes is tested with posterior probabilities based on MCMC analysis (see Methods). Nodes supported by posterior probabilities between 50–70% are marked with hash symbol (red) and nodes between 70–80%, 80–90% and .90% are marked with a star colored green, blue and red, respectively. Bootstrap support from maximum likelihood approach (PhyML) is indicated for the node that separates Rhodopsin and cAMP receptors. The edges marked with asterisk were found to be Rhodopsin like sequences (8) in HMM search, but classified as cAMP based on phylogeny and motifs. The motifs of those 8 sequences similar to the other cAMP sequences are shown in Figure 1. doi:10.1371/journal.pone.0029817.g002 PLoS ONE | www.plosone.org 5 January 2012 | Volume 7 | Issue 1 | e29817