Steroids are of universal occurrence, present variously as cell wall constituents and bioregulators. A number of bacteria, fungi, and photosynthetic vascular plants synthesize steroids that are hormonally active in the animal world. The cellular effect of such steroids in microbes and plants appears by and large to be comparable to that in mammals. Available evidence suggests that steroid action in botanical phyla is mediated via receptors organized in a manner similar to that seen in animals. Therefore, the ancestry of ligand induced transactivation via zinc finger proteins appears to date farther back than the early Cambrian burst of metazoan evolution 500 million years ago.
