Human G protein-coupled receptor (GPCR) signaling pathway proteins that are conserved across the diatom genomes and EST libraries. Conservation is based on BLAST sequence similarity criteria consisting of an e-value <10-5, <10-10, or 10-20 over a minimum alignment length of 100 amino acids unless specified otherwise. Homology to the G protein γ-subunit and RGS was identified using the Pfam database and HMMER. Note that this is an abbreviated representation of the GPCR signaling pathway that includes the primary components and a selection of the major downstream effectors. aDue to the absence of human homologs, the BLAST search space for GPCRs, the Gγ-subunit and RGS was expanded to include all organisms. Gα(i), Gi alpha subunit protein; Gα(q), Gq alpha subunit protein; Gα(s), Gs alpha subunit protein; Gα(12/13), Gi alpha subunit protein 12/13; GRK, G protein-coupled receptor kinase; MAPK/ERK, mitogen-activated protein kinases/extracellular signal-regulated kinases; NF-kB, nuclear factor-kappa B; PI3/PI4 kinases, phosphatidylinositide 3- and 4- kinases; PLCβ, phospholipase C beta; Raf, RAF proto-oncogene serine/threonine-protein kinase; Rap1GAP, Rap1-GTPase activating protein; RasGAP, Ras GTPase activating protein; RhoGEF, Rho guanine nucleotide exchange factor; RGS, regulator of G protein signaling.