Newly assembled snRNPs associate with coiled bodies before speckles, suggesting a nuclear snRNP maturation pathway

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Abstract

Background: Small nuclear ribonucleoproteins (snRNPs), which are essential components of the mRNA splicing machinery, comprise small nuclear RNAs, each complexed with a set of proteins. An early event in the maturation of snRNPs is the binding of the core proteins - the Sm proteins - to snRNAs in the cytoplasm followed by nuclear import. Immunolabelling with antibodies against Sm proteins shows that splicing snRNPs have a complex steady-state localisation within the nucleus, the result of the association of snRNPs with several distinct subnuclear structures. These include speckles, coiled bodies and nucleoli, in addition to a diffuse nucleoplasmic compartment. The reasons for snRNP accumulation in these different structures are unclear.

Results: When mammalian cells were microinjected with plasmids encoding the Sm proteins B, D1 and E, each tagged with either the green fluorescent protein (GFP) or yellow-shifted GFP (YFP), a pulse of expression of the tagged proteins was observed. In each case, the newly synthesised GFP/YFP-labelled snRNPs accumulated first in coiled bodies and nucleoli, and later in nuclear speckles. Mature snRNPs localised immediately to speckles upon entering the nucleus after cell division.

Conclusions: The complex nuclear localisation of splicing snRNPs results, at least in part, from a specific pathway for newly assembled snRNPs. The data demonstrate that the distribution of snRNPs between coiled bodies and speckles is directed and not random.

Original languageEnglish
Pages (from-to)1065-74
Number of pages10
JournalCurrent Biology
Volume9
Issue number19
DOIs
Publication statusPublished - 7 Oct 1999

Keywords

  • INTRANUCLEAR DISTRIBUTION
  • SPLICING SNRNPS
  • U1 SNRNA
  • NASCENT TRANSCRIPTS
  • MAMMALIAN-CELLS
  • SR PROTEINS
  • RNA
  • RIBONUCLEOPROTEINS
  • ORGANIZATION
  • NUCLEOLUS

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