title: MEKHLA, a novel domain with similarity to PAS domains, is fused to plant homeodomain-leucine zipper III proteins.
abstract: Homeodomain (HD) proteins play important roles in the development of plants, fungi, and animals. Here we identify a novel domain, MEKHLA, in the C terminus of HD-Leu zipper (HD-ZIP) III plant HD proteins that shares similarity with a group of bacterial proteins and a protein from the green alga Chlamydomonas reinhardtii. The group of bacterial MEKHLA proteins is found in cyanobacteria and other bacteria often found associated with plants. Phylogenetic analysis suggests that a MEKHLA protein transferred, possibly from a cyanobacterium or an early chloroplast, into the nuclear genome of an early plant in a first step, and attached itself to the C terminus of an HD-ZIP IV homeobox gene in a second step. Further position-specific iterated-BLAST searches with the bacterial MEKHLA proteins revealed a subregion within the MEKHLA domain that shares significant similarity with the PAS domain. The PAS domain is a sensory module found in many proteins through all kingdoms of life. It is involved in light, oxygen, and redox potential sensation. The fact that HD-ZIP III proteins are transcription factors that have this sensory domain attached to their C terminus uncovers a potential new signaling pathway in plants.
authors.affiliation: Department of Biosciences and Nutrition and Center for Genomics and Bioinformatics, Karolinska Institutet, SE-141 57 Huddinge, Sweden.
authors.forename: Krishanu
authors.initials: K
authors.lastname: Mukherjee
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Bürglin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics; D016825:Chlamydomonas reinhardtii / Q000235:genetics; D019143:Evolution, Molecular; D023281:Genomics; D018398:Homeodomain Proteins / Q000737:chemistry* / Q000235:genetics; D016350:Leucine Zippers; D008969:Molecular Sequence Data; D012275:Oryza / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D018398:Homeodomain Proteins; D010940:Plant Proteins; D015800:Protozoan Proteins