RESUMEN
DNA replication results in the doubling of the genome prior to cell division. This process requires the assembly of 50 or more protein factors into a replication fork. Here, we review recent structural and biochemical insights that start to explain how specific proteins recognize DNA replication origins, load the replicative helicase on DNA, unwind DNA, synthesize new DNA strands, and reassemble chromatin. We focus on the minichromosome maintenance (MCM2-7) proteins, which form the core of the eukaryotic replication fork, as this complex undergoes major structural rearrangements in order to engage with DNA, regulate its DNA-unwinding activity, and maintain genome stability.
Asunto(s)
Replicación del ADN/fisiología , Animales , Cromatina/metabolismo , ADN Helicasas/metabolismo , Replicación del ADN/genética , Evolución Molecular , Inestabilidad Genómica/genética , Humanos , Proteínas de Mantenimiento de Minicromosoma/genética , Proteínas de Mantenimiento de Minicromosoma/metabolismo , Origen de Réplica/fisiologíaRESUMEN
RNA polymerase III (RNAPIII) synthesizes most small RNAs, the most prominent being tRNAs. Although the basic mechanism of RNAPIII transcription is well understood, recent evidence suggests that additional proteins play a role in RNAPIII transcription. Here, we discovered by a genome-wide approach that Nab2, a poly(A)-binding protein important for correct poly(A) tail length and nuclear mRNA export, is present at all RNAPIII transcribed genes. The occupancy of Nab2 at RNAPIII transcribed genes is dependent on transcription. Using a novel temperature-sensitive allele of NAB2, nab2-34, we show that Nab2 is required for the occupancy of RNAPIII and TFIIIB at target genes. Furthermore, Nab2 interacts with RNAPIII, TFIIIB, and RNAPIII transcripts. Importantly, impairment of Nab2 function causes an RNAPIII transcription defect in vivo and in vitro. Taken together, we establish Nab2, an important mRNA biogenesis factor, as a novel player required for RNAPIII transcription by stabilizing TFIIIB and RNAPIII at promoters.
Asunto(s)
Regulación Fúngica de la Expresión Génica , Proteínas de Transporte Nucleocitoplasmático/metabolismo , ARN Polimerasa III/metabolismo , Proteínas de Unión al ARN/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Proteínas de Transporte Nucleocitoplasmático/genética , Regiones Promotoras Genéticas , Unión Proteica , ARN Polimerasa III/genética , Proteínas de Unión al ARN/genética , Proteínas de Saccharomyces cerevisiae/genéticaRESUMEN
Mutations in the l(3)mbt tumour suppressor result in overproliferation of Drosophila larval brains. Recently, the derepression of different gene classes in l(3)mbt mutants was shown to be causal for transformation. However, the molecular mechanisms of dL(3)mbt-mediated gene repression are not understood. Here, we identify LINT, the major dL(3)mbt complex of Drosophila. LINT has three core subunits-dL(3)mbt, dCoREST, and dLint-1-and is expressed in cell lines, embryos, and larval brain. Using genome-wide ChIP-Seq analysis, we show that dLint-1 binds close to the TSS of tumour-relevant target genes. Depletion of the LINT core subunits results in derepression of these genes. By contrast, histone deacetylase, histone methylase, and histone demethylase activities are not required to maintain repression. Our results support a direct role of LINT in the repression of brain tumour-relevant target genes by restricting promoter access.
Asunto(s)
Neoplasias Encefálicas/genética , Proteínas de Drosophila , Drosophila melanogaster/genética , Complejos Multiproteicos , Proteínas Represoras , Animales , Animales Modificados Genéticamente , Sitios de Unión , Línea Celular , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Regulación de la Expresión Génica , Genoma de los Insectos , Células Germinativas/metabolismo , Histonas/genética , Histonas/metabolismo , Larva/genética , Larva/metabolismo , Complejos Multiproteicos/genética , Complejos Multiproteicos/metabolismo , Mutación , Cromosomas Politénicos/genética , Interferencia de ARN , Proteínas Represoras/genética , Proteínas Represoras/metabolismoRESUMEN
RNA polymerase III (RNAPIII) synthesizes diverse, small, non-coding RNAs with many important roles in the cellular metabolism. One of the open questions of RNAPIII transcription is whether and how additional factors are involved. Recently, Nab2 was identified as the first messenger ribonucleoprotein particle (mRNP) biogenesis factor with a function in RNAPIII transcription.