Evolution of the GTP-cyclohydrolase I gene family in vertebrates. (a) Maximum-likelihood phylogeny of GchI protein sequences based on 268 AA positions (left). The tree is rooted with GchI from urochordates. Numbers at the branches denote bootstrap values (maximum likelihood/neighbor joining) above 50%. Groups (GchIa, GchIb, GchIc) were assigned according to genomic environment of gchI genes (right). GchIa and gchIb are both linked to members of the socs gene family (blue). GchIb is absent from mammalian and avian genomes, gchIc is only found in some teleost lineages. Dotted lines connect orthologous genes. (b) The gchIb region of teleosts and amphibian is syntenic to a chromosomal block in the genomes of mammals and bird lacking gchIb, suggesting that gchIb was lost secondarily in these lineages.