RESUMO
We determined the distribution of repressor-activator protein 1 (Rap1) and the accessory silencing proteins Sir2, Sir3 and Sir4 in vivo on the entire yeast genome, at a resolution of 2 kb. Rap1 is central to the cellular economy during rapid growth, targeting 294 loci, about 5% of yeast genes, and participating in the activation of 37% of all RNA polymerase II initiation events in exponentially growing cells. Although the DNA sequence recognized by Rap1 is found in both coding and intergenic sequences, the binding of Rap1 to the genome was highly specific to intergenic regions with the potential to act as promoters. This global phenomenon, which may be a general characteristic of sequence-specific transcriptional factors, indicates the existence of a genome-wide molecular mechanism for marking promoter regions.
Assuntos
Proteínas de Ligação a DNA/metabolismo , DNA/metabolismo , Genoma Fúngico , Mapeamento Físico do Cromossomo/métodos , Regiões Promotoras Genéticas/fisiologia , Saccharomyces cerevisiae/genética , Proteínas Reguladoras de Informação Silenciosa de Saccharomyces cerevisiae , Sítios de Ligação/genética , DNA Intergênico/metabolismo , Proteínas Fúngicas/metabolismo , Regulação da Expressão Gênica/fisiologia , Genes Fúngicos/fisiologia , Glicólise/genética , Histona Desacetilases/metabolismo , Fases de Leitura Aberta/fisiologia , Ligação Proteica/fisiologia , RNA Polimerase II/metabolismo , Proteínas Ribossômicas/genética , Saccharomyces cerevisiae/metabolismo , Sirtuína 2 , Sirtuínas , Telômero/metabolismo , Transativadores/metabolismoRESUMO
The dosage compensation machinery of Caenorhabditis elegans is targeted specifically to the X chromosomes of hermaphrodites (XX) to reduce gene expression by half. Many of the trans-acting factors that direct the dosage compensation machinery to X have been identified, but none of the proposed cis-acting X chromosome-recognition elements needed to recruit dosage compensation components have been found. To study X chromosome recognition, we explored whether portions of an X chromosome attached to an autosome are competent to bind the C. elegans dosage compensation complex (DCC). To do so, we devised a three-dimensional in situ approach that allowed us to compare the volume, position, and number of chromosomal and subchromosomal bodies bound by the dosage compensation machinery in wild-type XX nuclei and XX nuclei carrying an X duplication. The dosage compensation complex was found to associate with a duplication of the right 30% of X, but the complex did not spread onto adjacent autosomal sequences. This result indicates that all the information required to specify X chromosome identity resides on the duplication and that the dosage compensation machinery can localize to a site distinct from the full-length hermaphrodite X chromosome. In contrast, smaller duplications of other regions of X appeared to not support localization of the DCC. In a separate effort to identify cis-acting X recognition elements, we used a computational approach to analyze genomic DNA sequences for the presence of short motifs that were abundant and overrepresented on X relative to autosomes. Fourteen families of X-enriched motifs were discovered and mapped onto the X chromosome.
Assuntos
Proteínas de Caenorhabditis elegans , Caenorhabditis elegans/genética , Cromossomos/genética , Transtornos do Desenvolvimento Sexual/genética , Mecanismo Genético de Compensação de Dose , Translocação Genética , Cromossomo X/genética , Animais , Caenorhabditis elegans/embriologia , Proteínas de Transporte/fisiologia , Proteínas de Ciclo Celular/fisiologia , Núcleo Celular/ultraestrutura , Proteínas Cromossômicas não Histona/fisiologia , Proteínas de Ligação a DNA/fisiologia , Desenvolvimento Embrionário , Duplicação Gênica , Regulação da Expressão Gênica , Proteínas de Helminto/fisiologia , Processamento de Imagem Assistida por Computador , Substâncias Macromoleculares , Microscopia Confocal , Proteínas Nucleares/fisiologiaRESUMO
We show that a functional component of the C. elegans mitotic machinery regulates X chromosome gene expression. This protein, MIX-1, is a member of the dosage compensation complex that associates specifically with hermaphrodite X chromosomes to reduce their gene expression during interphase. MIX-1 also associates with all mitotic chromosomes to ensure their proper segregation. Both dosage compensation and mitosis are severely disrupted by mix-1 mutations. MIX-1 belongs to the SMC protein family required for mitotic chromosome condensation and segregation in yeast and frogs. Thus, an essential, conserved component of mitotic chromosomes has been recruited to the dosage compensation process. Rather than dosage compensation and mitosis being achieved by two separate sets of related genes, these two processes share an identical component, indicating a common mechanism for establishing higher order chromosome structure and proper X chromosome gene expression.
Assuntos
Proteínas de Caenorhabditis elegans , Caenorhabditis elegans/genética , Proteínas de Ciclo Celular/genética , Mecanismo Genético de Compensação de Dose , Genes de Helmintos/genética , Proteínas de Helminto/genética , Mitose/genética , Sequência de Aminoácidos , Animais , Caenorhabditis elegans/embriologia , Proteínas de Ciclo Celular/análise , Proteínas de Ciclo Celular/química , Transtornos do Desenvolvimento Sexual , Feminino , Proteínas de Helminto/análise , Proteínas de Helminto/química , Interfase , Masculino , Modelos Genéticos , Dados de Sequência Molecular , Peso Molecular , Mutação , Homologia de Sequência de Aminoácidos , Cromossomo X/químicaRESUMO
The DPY-26 protein is required in the nematode Caenorhabditis elegans for X-chromosome dosage compensation as well as for proper meiotic chromosome segregation. DPY-26 was shown to mediate both processes through its association with chromosomes. In somatic cells, DPY-26 associates specifically with hermaphrodite X chromosomes to reduce their transcript levels. In germ cells, DPY-26 associates with all meiotic chromosomes to mediate its role in chromosome segregation. The X-specific localization of DPY-26 requires two dosage compensation proteins (DPY-27 and DPY-30) and two proteins that coordinately control both sex determination and dosage compensation (SDC-2 and SDC-3).
Assuntos
Proteínas de Caenorhabditis elegans , Caenorhabditis elegans/fisiologia , Cromossomos/fisiologia , Mecanismo Genético de Compensação de Dose , Proteínas de Helminto/fisiologia , Meiose , Animais , Caenorhabditis elegans/embriologia , Caenorhabditis elegans/genética , Proteínas de Transporte/fisiologia , Núcleo Celular/química , Transtornos do Desenvolvimento Sexual , Desenvolvimento Embrionário , Feminino , Expressão Gênica , Genes de Helmintos , Células Germinativas/fisiologia , Proteínas de Helminto/análise , Proteínas de Helminto/genética , Masculino , Dados de Sequência Molecular , Mutação , Proteínas Nucleares/fisiologia , Cromossomo X/fisiologiaRESUMO
In nematodes, flies, and mammals, dosage compensation equalizes X-chromosome gene expression between the sexes through chromosome-wide regulatory mechanisms that function in one sex to adjust the levels of X-linked transcripts. Here, a dosage compensation complex was identified in the nematode Caenorhabditis elegans that reduces transcript levels from the two X chromosomes in hermaphrodites. This complex contains at least four proteins, including products of the dosage compensation genes dpy-26 and dpy-27. Specific localization of the complex to the hermaphrodite X chromosomes is conferred by XX-specific regulatory genes that coordinately control both sex determination and dosage compensation.
