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

Curr Biol. 1999 Oct 7;9(19):1065-74. doi: 10.1016/s0960-9822(99)80475-8.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Autoantigens / metabolism
  • Bacterial Proteins / metabolism
  • Cell Nucleolus / physiology
  • Cell Nucleus / metabolism*
  • Coiled Bodies / metabolism*
  • Green Fluorescent Proteins
  • HeLa Cells
  • Humans
  • Kinetics
  • Luminescent Proteins / metabolism
  • Microscopy, Confocal
  • Recombinant Fusion Proteins / metabolism
  • Ribonucleoproteins, Small Nuclear / metabolism*
  • Saccharomyces cerevisiae Proteins*
  • Time Factors
  • Tumor Cells, Cultured
  • snRNP Core Proteins


  • Autoantigens
  • Bacterial Proteins
  • Luminescent Proteins
  • Recombinant Fusion Proteins
  • Ribonucleoproteins, Small Nuclear
  • SME1 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • snRNP Core Proteins
  • yellow fluorescent protein, Bacteria
  • Green Fluorescent Proteins