The structures of HD-START proteins from plants in comparison to classic nuclear receptors from animals. (a) Plant-specific HD-ZLZ START and HD-ZIP START proteins are transcription factors comprised of an amino-terminal HD DNA-binding domain preceding START, a putative lipid/sterol-binding domain. (b) Nuclear receptors, which are found only in animal genomes, comprise a zinc finger DNA-binding domain of the C4 (two domain) type (zf-C4), and a carboxy-terminal hormone receptor (HR) domain that binds steroid ligands. Members of the nuclear receptor superfamily bind other lipophilic molecules, such as retinoic acid or thyroxine.
Schrick et al. Genome Biology 2004 5:R41 doi:10.1186/gb-2004-5-6-r41