RESUMO
The yeast cell nucleus has previously been shown to be divided into two regions by a variety of microscopic approaches. We used antibodies specific for the 2,2,7-trimethylguanosine cap structure of small nuclear ribonucleic acids (snRNAs) and for a protein component of small nuclear ribonucleoprotein particles to identify the distribution of small nuclear ribonucleoprotein particles within the yeast cell nucleus. These studies were performed with the fission yeast Schizosaccharomyces pombe and the budding yeast Saccharomyces cerevisiae. By using immunofluorescence microscopy and immunoelectron microscopy, most of the abundant snRNAs were localized to the portion of the nucleus which has heretofore been referred to as the nucleolus. This distribution of snRNAs is different from that found in mammalian cells and suggests that the nucleolar portion of the yeast nucleus contains functional domains in addition to those associated with RNA polymerase I activity.
Assuntos
Núcleo Celular/metabolismo , Precursores de RNA/genética , Processamento Pós-Transcricional do RNA , Saccharomyces cerevisiae/genética , Schizosaccharomyces/genética , Anticorpos , Núcleo Celular/ultraestrutura , Imunofluorescência , Guanosina/análogos & derivados , Guanosina/análise , Imuno-Histoquímica , Microscopia Eletrônica , RNA Nuclear Pequeno/análise , RNA Nuclear Pequeno/genética , Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/ultraestrutura , Schizosaccharomyces/metabolismo , Schizosaccharomyces/ultraestrutura , Esferoplastos/metabolismo , Esferoplastos/ultraestruturaRESUMO
Transport of mRNA from the nucleus to the cytoplasm plays an important role in gene expression in eukaryotic cells. In wild-type Schizosaccharomyces pombe cells poly(A)+ RNA is uniformly distributed throughout the nucleoplasm and cytoplasm. However, we found that a severe heat shock blocks mRNA transport in S. pombe, resulting in the accumulation of bulk poly(A)+ RNA, as well as a specific intron-less transcript, in the nucleoli. Pretreatment of cells with a mild heat shock, which induces heat shock proteins, before a severe heat shock protects the mRNA transport machinery and allows mRNA transport to proceed unimpeded. In heat-shocked S. pombe cells, the nucleolar region condensed into a few compact structures. Interestingly, poly(A)+ RNA accumulated predominantly in the condensed nucleolar regions of the heat-shocked cells. These data suggest that the yeast nucleolus may play a role in mRNA transport in addition to its roles in rRNA synthesis and preribosome assembly.
Assuntos
Nucléolo Celular/metabolismo , RNA Mensageiro/metabolismo , Schizosaccharomyces/metabolismo , Sequência de Bases , Nucléolo Celular/efeitos dos fármacos , Nucléolo Celular/ultraestrutura , Cicloeximida/farmacologia , Temperatura Alta , Hibridização In Situ , Microscopia Eletrônica , Dados de Sequência Molecular , Sondas de Oligonucleotídeos , Schizosaccharomyces/ultraestruturaRESUMO
Transport of mRNA from the nucleus to the cytoplasm plays an important role in gene expression in eukaryotic cells. In wild-type Schizosaccharomyces pombe cells poly(A)+ RNA is uniformly distributed throughout the nucleoplasm and cytoplasm. However, we found that a severe heat shock blocks mRNA transport in S. pombe, resulting in the accumulation of bulk poly(A)+ RNA, as well as a specific intron-less transcript, in the nucleoli. Pretreatment of cells with a mild heat shock, which induces heat shock proteins, before a severe heat shock protects the mRNA transport machinery and allows mRNA transport to proceed unimpeded. In heat-shocked S. pombe cells, the nucleolar region condensed into a few compact structures. Interestingly, poly(A)+ RNA accumulated predominantly in the condensed nucleolar regions of the heat-shocked cells. These data suggest that the yeast nucleolus may play a role in mRNA transport in addition to its roles in rRNA synthesis and preribosome assembly.