Nucleolus

About: Nucleolus is a research topic. Over the lifetime, 5873 publications have been published within this topic receiving 232435 citations. The topic is also known as: GO:0005730 & cell nucleolus.

C1D and hMtr4p associate with the human exosome subunit PM/Scl-100 and are involved in pre-rRNA processing

Abstract: The exosome is a complex of 3′–5′ exoribonucleases and RNA-binding proteins, which is involved in processing or degradation of different classes of RNA. Previously, the characterization of purified exosome complexes from yeast and human cells suggested that C1D and KIAA0052/hMtr4p are associated with the exosome and thus might regulate its functional activities. Subcellular localization experiments demonstrated that C1D and KIAA0052/hMtr4p co-localize with exosome subunit PM/Scl-100 in the nucleoli of HEp-2 cells. Additionally, the nucleolar accumulation of C1D appeared to be dependent on PM/Scl-100. Protein–protein interaction studies showed that C1D binds to PM/Scl-100, whereas KIAA0052/hMtr4p was found to interact with MPP6, a previously identified exosome-associated protein. Moreover, we demonstrate that C1D, MPP6 and PM/Scl-100 form a stable trimeric complex in vitro. Knock-down of C1D, MPP6 and KIAA0052/hMtr4p by RNAi resulted in the accumulation of 3′-extended 5.8S rRNA precursors, showing that these proteins are required for rRNA processing. Interestingly, C1D appeared to contain RNA-binding activity with a potential preference for structured RNAs. Taken together, our results are consistent with a role for the exosome-associated proteins C1D, MPP6 and KIAA052/hMtr4p in the recruitment of the exosome to pre-rRNA to mediate the 3′ end processing of the 5.8S rRNA.

Biogenesis of the signal recognition particle (SRP) involves import of SRP proteins into the nucleolus, assembly with the SRP-RNA, and Xpo1p-mediated export.

Abstract: The signal recognition particle (SRP) targets nascent secretory proteins to the ER, but how and where the SRP assembles is largely unknown. Here we analyze the biogenesis of yeast SRP, which consists of an RNA molecule (scR1) and six proteins, by localizing all its components. Although scR1 is cytoplasmic in wild-type cells, nuclear localization was observed in cells lacking any one of the four SRP “core proteins” Srp14p, Srp21p, Srp68p, or Srp72p. Consistently, a major nucleolar pool was detected for these proteins. Sec65p, on the other hand, was found in both the nucleoplasm and the nucleolus, whereas Srp54p was predominantly cytoplasmic. Import of the core proteins into the nucleolus requires the ribosomal protein import receptors Pse1p and Kap123p/Yrb4p, which might, thus, constitute a nucleolar import pathway. Nuclear export of scR1 is mediated by the nuclear export signal receptor Xpo1p, is distinct from mRNA transport, and requires, as evidenced by the nucleolar accumulation of scR1 in a dis3/rrp44 exosome component mutant, an intact scR1 3′ end. A subset of nucleoporins, including Nsp1p and Nup159p (Rat7p), are also necessary for efficient translocation of scR1 from the nucleus to the cytoplasm. We propose that assembly of the SRP requires import of all SRP core proteins into the nucleolus, where they assemble into a pre-SRP with scR1. This particle can then be targeted to the nuclear pores and is subsequently exported to the cytoplasm in an Xpo1p-dependent way.

The Sites of Nucleolus Formation in Human Pachytene Chromosomes

Abstract: Studies of the pachytene stage of human meiosis in young adult males show that the principal nucleoli are associated with the terminal chromomeres of certain bivalents. These findings are reconcilable

On the redundancy of dna complementary to amino acid transfer rna and its absence from the nucleolar organizer region of drosophila melanogaster

Abstract: MOLECULAR hybridization (HALL and SPIEGELMAN 1961 ) of labeled ribosomal RNA (r-RNA) with DNA in D. mlanogaster has revealed (VERMEULEN and ATWOOD 1965; RITOSSA and SPIEGELMAN 1965) that, as in the bacteria (YANKOFSKY and SPIEGELMAN 1962a, b, 1963), approximately 0.27% of the DNA is complementary to r-RNA. This DNA is believed to constitute the ensemble of templates for the transcription of r-RNA and may be referred to as the r-DNA. The amount of r-DNA per haploid Drosophila genome is sufficient to complement at least 130 molecules each of 18s and 28s r-RNA. Inversions in the X chromosome of Drosophila melanoguster are available (SIDOROV 1930; STURTEVANT and BEADLE 1936; MULLER et al. 1937) from which one can derive X chromosomes possessing duplications or deletions of a heterochromatic region which includes the nucleolus organizer (NO). With these chromosomes, flies can be obtained which have from one to four doses of the NO region. With DNA from such flies, annealing experiments demonstrated ( RITOSSA and SPIEGELMAN 1965) that the amount of r-RNA hybridizable per unit of DNA was directly proportional to the dosage of the NO region per genome. These data indicated then that the DNA sequences complementary to the ribosomal RNA are confined to the segment contained in the deletion or duplication employed. The existence in bacteria of DNA complementary to amino acid transfer RNA (t-RNA) has been established ( GIACOMONI and SPIEGELMAN 1962; GOODMAN and RICH 1962). However, this issue has thus far not been taken up in the higher forms. It is, in principle, readily resolvable by molecular hybridization with suitably labeled and purified t-RNA. The D. melanogaster DNA used in the studies on ribosomal RNA permits the performance of the necessary experiments as well as others relevant to the following two questions: (1 ) What proportion of the D. melanogaster genome is complementary to t-RNA? (2) Are the DNA complements of t-RNA localized in the same region as those of the r-RNA? An answer to the first question is pertinent to possible interpretations of the 130-fold redundancy in ribosomal DNA complements. The second question is of obvious interest and gains particular importance from recent reports of t-RNA ' The In\\estigations reported here were supported by Grants GB-2169, GB-2700, GB-296 from the National Science Foundation, and by Public Health Service Research Grant No CA-01094 from the National Cancer Institute On leave from the International Laboratory of Genetics and Biophysics

DEDD, a novel death effector domain-containing protein, targeted to the nucleolus.

Abstract: The CD95 signaling pathway comprises proteins that contain one or two death effector domains (DED), such as FADD/Mort1 or caspase-8. Here we describe a novel 37 kDa protein, DEDD, that contains an N-terminal DED. DEDD is highly conserved between human and mouse (98. 7% identity) and is ubiquitously expressed. Overexpression of DEDD in 293T cells induced weak apoptosis, mainly through its DED by which it interacts with FADD and caspase-8. Endogenous DEDD was found in the cytoplasm and translocated into the nucleus upon stimulation of CD95. Immunocytological studies revealed that overexpressed DEDD directly translocated into the nucleus, where it co-localizes in the nucleolus with UBF, a basal factor required for RNA polymerase I transcription. Consistent with its nuclear localization, DEDD contains two nuclear localization signals and the C-terminal part shares sequence homology with histones. Recombinant DEDD binds to both DNA and reconstituted mononucleosomes and inhibits transcription in a reconstituted in vitro system. The results suggest that DEDD is a final target of a chain of events by which the CD95-induced apoptotic signal is transferred into the nucleolus to shut off cellular biosynthetic activities.