title: The Arabidopsis thaliana HY1 locus, required for phytochrome-chromophore biosynthesis, encodes a protein related to heme oxygenases.
abstract: The hy1 mutants of Arabidopsis thaliana fail to make the phytochrome-chromophore phytochromobilin and therefore are deficient in a wide range of phytochrome-mediated responses. Because this defect can be rescued by feeding seedlings biliverdin IXalpha, it is likely that the mutations affect an enzyme that converts heme to this phytochromobilin intermediate. By a combination of positional cloning and candidate-gene isolation, we have identified the HY1 gene and found it to be related to cyanobacterial, algal, and animal heme oxygenases. Three independent alleles of hy1 contain DNA lesions within the HY1 coding region, and a genomic sequence spanning the HY1 locus complements the hy1-1 mutation. HY1 is a member of a gene family and is expressed in a variety of A. thaliana tissues. Based on its homology, we propose that HY1 encodes a higher-plant heme oxygenase, designated AtHO1, responsible for catalyzing the reaction that opens the tetrapyrrole ring of heme to generate biliverdin IXalpha.
authors.affiliation: Laboratory of Genetics and the Cellular and Molecular Biology Program, University of Wisconsin, 1575 Linden Drive, Madison, WI 53706, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Davis
authors.forename: J
authors.initials: J
authors.lastname: Kurepa
authors.forename: R D
authors.initials: RD
authors.lastname: Vierstra
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D001483:Base Sequence; D001664:Biliverdine / Q000378:metabolism; D003001:Cloning, Molecular; D018388:Codon, Terminator; D000458:Cyanobacteria / Q000201:enzymology / Q000235:genetics; D017931:DNA Primers; D056890:Eukaryota / Q000201:enzymology / Q000235:genetics; D017343:Genes, Plant; D005816:Genetic Complementation Test; D006419:Heme Oxygenase (Decyclizing) / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D005810:Multigene Family; D016296:Mutagenesis; D010834:Phytochrome / Q000096:biosynthesis*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D018388:Codon, Terminator; D017931:DNA Primers; D010834:Phytochrome; D006419:Heme Oxygenase (Decyclizing); D001664:Biliverdine