RESUMO
The structure of the gene encoding human hexabrachion (tenascin) has been determined from overlapping clones isolated from a human genomic bacteriophage library. The genomic inserts were characterized by restriction mapping, Southern blot analysis, PCR, and DNA sequencing. The coding region of the hexabrachion gene spans approximately 80 kilobases of DNA and consists of 27 exons separated by 26 introns. The exon-intron structure supports a hypothesis based on the cDNA sequence that the hexabrachion gene is an assembly of DNA modules that are also found elsewhere in the genome. Single exons may encode a module, a portion of a module, or a group of modules. The 15 type III units similar to those found in fibronectin are each encoded either by a single exon or by two exons interrupted by an intron. All type III units known to be spliced out of the smaller forms of the protein are encoded by one exon. The fibrinogen-like domain of 210 amino acids is encoded by five exons. The 14.5 epidermal growth factor-like repeats are all encoded by a single exon.
Assuntos
Moléculas de Adesão Celular Neuronais/genética , Proteínas da Matriz Extracelular/genética , Sequência de Aminoácidos , Sequência de Bases , Clonagem Molecular , Genes , Humanos , Íntrons , Dados de Sequência Molecular , Alinhamento de Sequência , TenascinaRESUMO
Utilizing a cDNA clone encoding the oligodendrocyte-myelin glycoprotein (OMgp) to screen a human genomic DNA library, we have obtained a clone that contains the OMgp gene. The genomic clone was restriction mapped and the OMgp gene and its 5' and 3' flanking regions were sequenced. A single intron is found in the 5' untranslated region of the gene, while the coding region is uninterrupted by an intron. This placement of a single intron in the OMgp gene is identical to that of the gene for the alpha-chain of platelet glycoprotein Ib, which, along with OMgp, belongs to a family of proteins sharing two distinct structural domains: an NH2-terminal cysteine-rich domain and an adjacent domain of tandem leucine-rich repeats. Hence, it is possible that this family of proteins is not only related in terms of primary structure, but also through similar gene structure. Sequence comparison of the 5' and 3' flanking regions did not reveal striking similarities to other DNA sequences, and no obvious promoter elements were noted. By hybridization of the genomic clone to metaphase cells, we have localized the human OMgp gene to chromosome 17 bands q11-12, a region to which the neurofibromatosis type 1 gene has been previously mapped.
Assuntos
Cromossomos Humanos Par 17 , Genes , Glicoproteínas de Membrana/genética , Glicoproteína Associada a Mielina , Sequência de Aminoácidos , Sequência de Bases , Mapeamento Cromossômico , Proteínas Ligadas por GPI , Biblioteca Gênica , Humanos , Íntrons , Dados de Sequência Molecular , Proteínas da Mielina , Glicoproteína Mielina-Oligodendrócito , Proteínas do Tecido Nervoso/genética , Hibridização de Ácido Nucleico , Sondas de Oligonucleotídeos , Regiões Promotoras Genéticas , Mapeamento por Restrição , Homologia de Sequência do Ácido Nucleico , TATA BoxRESUMO
Using analysis of rodent-human somatic cell hybrids as well as in situ hybridization of hexabrachion cDNA probes to normal human metaphase chromosomes, we have localized the human hexabrachion gene to chromosome 9, bands q32-q34. We also put forward the hypothesis that there has been a recent reduplication of a small segment of the human hexabrachion gene. We support this hypothesis by comparison of codon usage in this segment of the gene to codon usage in the remainder of the gene. This hypothesis is also supported by comparison of the sequence of human hexabrachion to that of the chicken hexabrachion. In addition, the latter comparison shows that the reduplication most likely occurred after the divergence of mammalian and avian species.
