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A more recent version of this article appeared on August 1, 2004
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Submitted on March 25, 2004
Revised on May 20, 2004
Accepted on May 20, 2004
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*Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724; and
Amgen Center, Thousand Oaks, California 91320-1789
Monitoring Editor: Joseph Gall
A variety of proteins involved in gene expression have been localized within mammalian cell nuclei in a speckled distribution that predominantly corresponds to interchromatin granule clusters (IGCs). We have applied a mass spectrometry strategy to identify the protein composition of this nuclear organelle purified from mouse liver nuclei. Using this approach we have identified 146 proteins, many of which had already been shown to be localized to IGCs, or their functions are common to other already identified IGC proteins. In addition, we identified 32 proteins for which only sequence information is available and thus these represent novel IGC protein candidates. We find that 54% of the identified IGC proteins have known functions in pre-mRNA splicing. In combination with proteins involved in other steps of pre-mRNA processing, 81% of the identified IGC proteins are associated with RNA metabolism. In addition, proteins involved in transcription, as well as several other cellular functions, have been identified in the IGC fraction. However, the predominance of pre-mRNA processing factors supports the proposed role of IGCs as assembly, modification and/or storage sites for proteins involved in pre-mRNA processing.
Present address: Department of Regeneration Medicine, Institute of Molecular Embryology and Genetics, Kumamoto University, 2-2-1 Honjo, Kumamoto-shi, Kumamoto 860-0811, Japan
Corresponding author.