Serine/threonine phosphatase 1 modulates the subnuclear distribution of pre-mRNA splicing factors.
HeLa cell nuclei were permeabilized and reconstituted with nuclear extract to identify soluble nuclear factors which play a role in the organization of pre-mRNA splicing factors in the mammalian cell nucleus. Permeabilized nuclei reconstituted with nuclear extract were active in transcription and DNA replication and nuclear speckles containing pre-mRNA splicing factors were maintained over several hours independent of soluble nuclear components. The characteristic rounding up of nuclear speckles in response to inhibition of RNA polymerase II seen in vivo was reproduced in permeabilized cells and was strictly dependent on a catalytic activity present in the nuclear extract. By inhibitor titration experiments and sensitivity to inhibitor 2, this activity was identified as a member of the serine/threonine protein phosphatase 1 family (PP1). Interference with PP1 activity affected the distribution of pre-mRNA splicing factors in transcriptionally active, permeabilized cells, and excess PP1 activity caused increased dephosphorylation of SR proteins in nuclear speckles. These data show that the dynamic reorganization of the mammalian cell nucleus can be studied in permeabilized cells and that PP1 is involved in the rounding up of speckles as well as the overall organization of pre-mRNA splicing factors in the mammalian cell nucleus.
Cold Spring Harbor Laboratory, New York 11724, USA.
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D000546:Amanitins / Q000494:pharmacology; D002463:Cell Membrane Permeability; D002467:Cell Nucleus / Q000201:enzymology* / Q000648:ultrastructure; D006367:HeLa Cells; D006801:Humans; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000502:physiology; D009687:Nuclear Proteins / Q000502:physiology*; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D011506:Proteins / Q000494:pharmacology; D012319:RNA Polymerase II / Q000037:antagonists & inhibitors; D012322:RNA Precursors / Q000378:metabolism*; D012326:RNA Splicing; D000097847:Protein Phosphatase Inhibitory Proteins
D000546:Amanitins; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases; D011506:Proteins; D012319:RNA Polymerase II; D012322:RNA Precursors; C024833:protein phosphatase inhibitor-2; D000097847:Protein Phosphatase Inhibitory Proteins