title: The sequence of Locusta RXR, homologous to Drosophila Ultraspiracle, and its evolutionary implications.
abstract: The cellular response to steroid hormones is mediated by nuclear receptors which act by regulating transcription. In Drosophila melanogaster, the receptor for the insect molting hormone, 20-hydroxyecdysone, is a heterodimer composed of the Ecdysone Receptor and Ultraspiracle (USP) proteins. The DNA binding domains of arthropod USPs and their vertebrate homologs, the retinoid X receptor (RXR) family, are highly conserved. The ligand binding domain sequences, however, divide into two distinct groups. One group consists of sequences from members of the holometabolous higher insect orders Diptera and Lepidoptera, the other of sequences from vertebrates, a crab and a tick. We here report the sequence of an RXR/USP from the hemimetabolous orthopteran, Locusta migratoria. The locust RXR/USP ligand binding domain clearly falls in the vertebrate-crab-tick rather than the dipteran-lepidopteran group. The reason for the evolutionarily abrupt divergence of the dipteran and lepidopteran sequences is unknown, but it could be a change in the type of ligand bound or the loss of ligand altogether.
authors.affiliation: Molecular Genetics and Evolution Group, Research School of Biological Sciences, Australian National University, P.O. Box 475, Canberra, ACT 2601, Australia.
authors.forename: D C
authors.initials: DC
authors.lastname: Hayward
authors.forename: M J
authors.initials: MJ
authors.lastname: Bastiani
authors.forename: J W
authors.initials: JW
authors.lastname: Trueman
authors.forename: J W
authors.initials: JW
authors.lastname: Truman
authors.forename: L M
authors.initials: LM
authors.lastname: Riddiford
authors.forename: E E
authors.initials: EE
authors.lastname: Ball
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics*; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000235:genetics*; D019143:Evolution, Molecular; D006110:Grasshoppers / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D010802:Phylogeny; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry / Q000235:genetics; D018168:Receptors, Retinoic Acid / Q000737:chemistry / Q000235:genetics*; D047488:Retinoid X Receptors; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics*
chemical_list: D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D014157:Transcription Factors; C066030:USP protein, Drosophila