RESUMO
Proteins with seven transmembrane segments (7TM) define a superfamily of receptors (7TM receptors) sharing the same topology: an extracellular N-terminus, three extramembranous loops on either side of the plasma membrane, and a cytoplasmic C-terminal tail. Upon ligand binding, cytoplasmic portions of the activated receptor interact with heterotrimeric G-coupled proteins to induce various second messengers. A small group, recently recognized on the basis of homologous primary amino acid sequences, comprises receptors to hormones of the secretin/vasoactive intestinal peptide/glucagon family, parathyroid hormone and parathyroid hormone-related peptides, growth hormone-releasing factor, corticotropin-releasing factor, and calcitonin. A cDNA, extracted from a neuroectodermal cDNA library, was predicted to encode a new 886-amino-acid protein with three distinct domains. The C-terminal third contains the seven hydrophobic segments and characteristic residues that allow the protein to be readily aligned with the various hormone receptors in the family. Six egf-like modules, at the N-terminus of the predicted mature protein, are separated from the transmembrane segments by a serine/threonine-rich domain, a feature reminiscent of mucin-like, single-span, integral membrane glycoproteins with adhesive properties. Because of its unique characteristics, this putative egf module-containing, mucin-like hormone receptor has been named EMR1. Southern analysis of a panel of somatic cell hybrids and fluorescence in situ hybridization have assigned the EMR1 gene to human chromosome 19p13.3.
Assuntos
Genes , Glicoproteínas de Membrana/genética , Mucinas/genética , Família Multigênica , Sequência de Aminoácidos , Animais , Sequência de Bases , Proteínas de Ligação ao Cálcio , Cromossomos Humanos Par 19 , Sequência Consenso , Cricetinae , DNA Complementar/genética , Fator de Crescimento Epidérmico/química , Humanos , Células Híbridas , Glicoproteínas de Membrana/química , Dados de Sequência Molecular , Mucinas/química , Conformação Proteica , RNA Nuclear Heterogêneo/genética , Receptores de Superfície Celular/química , Receptores Acoplados a Proteínas G , Alinhamento de Sequência , Homologia de Sequência de AminoácidosRESUMO
An important step ensuring the fidelity in protein biosynthesis is the aminoacylation of tRNAs by aminoacyl-tRNA synthetases. The accuracy of this process rests on a family of 20 enzymes, one for each amino acid. One exception is the formation of Gln-tRNA(Gln) that can be accomplished by two different pathways: aminoacylation of tRNA(Gln) with Gln by glutaminyl-tRNA synthetase (GlnRS; EC 6.1.1.18) or transamidation of Glu from Glu-tRNA(Gln) mischarged by glutamyl-tRNA synthetase (GluRS; EC 6.1.1.17). The latter pathway is widespread among bacteria and organelles that, accordingly, lack GlnRS. However, some bacterial species, such as Escherichia coli, do possess a GlnRS activity, which is responsible for Gln-tRNA(Gln) formation. In the cytoplasm of eukaryotic cells, both GluRS and GlnRS activities can be detected. To gain more insight into the evolutionary relationship between GluRS and GlnRS enzyme species, we have now isolated and characterized a human cDNA encoding GlnRS. The deduced amino acid sequence shows a strong similarity with other known GlnRSs and with eukaryotic GluRSs. A molecular phylogenetic analysis was conducted on the 14 GlxRS (GluRS or GlnRS) sequences available to date. Our data suggest that bacterial GlnRS has a eukaryotic origin and was acquired by a mechanism of horizontal gene transfer.
Assuntos
Aminoacil-tRNA Sintetases/genética , Glutamato-tRNA Ligase/genética , Família Multigênica , Sequência de Aminoácidos , Proteínas de Bactérias/genética , Cromossomos Humanos Par 3 , Clonagem Molecular , DNA Complementar/genética , Proteínas Fúngicas/genética , Genes , Humanos , Dados de Sequência Molecular , Filogenia , Alinhamento de Sequência , Homologia de Sequência de AminoácidosRESUMO
Type VI collagen is a heterotrimer composed of three polypeptide chains, alpha 1(VI), alpha 2(VI), and alpha 3(VI). By immunological screening of an expression cDNA library, human cDNAs specific for each chain were isolated and characterized. Major mRNA species encoding these chains have a size of 4.2 kb (alpha 1), 3.5 kb (alpha 2), and 8.5 kb (alpha 3). The cDNA clones were also used to map the genes on human chromosomes by somatic cell hybrid analysis and in situ hybridization. The alpha 1 (VI) and alpha 2(VI) collagen genes were both located on chromosome 21, in band q223. This represents a third example of a possible physical proximity of two collagen loci. The alpha 3(VI) collagen gene was localized to chromosome 2, in the region 2q37. The alpha 3(VI) collagen gene is the fifth extracellular matrix gene to be localized to 2q, as four other extracellular matrix genes--i.e., the alpha 1(III) and alpha 2(V) collagen genes, the elastin gene, and the fibronectin gene--have been previously mapped to the distal region of the long arm of chromosome 2.
Assuntos
Mapeamento Cromossômico , Colágeno/genética , Genes , Sequência de Aminoácidos , Animais , Sequência de Bases , Bandeamento Cromossômico , Cromossomos Humanos Par 2 , Cromossomos Humanos Par 21 , DNA/genética , Humanos , Células Híbridas , Cariotipagem , Camundongos , Dados de Sequência Molecular , Hibridização de Ácido NucleicoRESUMO
Starting from a chromosome-specific DNA library, we have isolated a human chromosome-specific satellite DNA sequence. This sequence of 635 base pairs (bp) consists of 3.7 alpha DNA monomers of 170-171 bp. Under high stringency it hybridizes to the centromere of chromosome 3 in a region composed of 2,750 bp tandem repeats characterized by the regular spacing of Hind III and TaqI restriction enzyme recognition sites. It has diverged and undergone amplification after the human speciation. The amplification allows an easy monitoring of the chromosome 3 centromere by in situ hybridization with a nonradioactive probe.
Assuntos
Centrômero , Cromossomos Humanos Par 3 , Cromossomos , Clonagem Molecular , DNA Satélite/genética , Animais , Mapeamento Cromossômico , Heterocromatina , Humanos , Imunoquímica , Dados de Sequência Molecular , Hibridização de Ácido Nucleico , Polimorfismo de Fragmento de Restrição , Primatas , Homologia de Sequência do Ácido Nucleico , Especificidade da EspécieRESUMO
A specific enzyme immunoassay of uroporphyrinogen decarboxylase was developed and applied to the detection of the human enzyme in man-rodent somatic cell hybrids. This method allowed to assign the gene for uroporphyrinogen decarboxylase to human chromosome 1.