The survival of motor neurons (SMN) protein interacts with the snoRNP proteins fibrillarin and GAR1.
BACKGROUND
The survival of motor neurons (SMN) protein is the protein product of the spinal muscular atrophy (SMA) disease gene. SMN and its associated proteins Gemin2, Gemin3, and Gemin4 form a large complex that plays a role in snRNP assembly, pre-mRNA splicing, and transcription. The functions of SMN in these processes are mediated by a direct interaction of SMN with components of these machineries, such as Sm proteins and RNA helicase A.


RESULTS
We show that SMN binds directly to fibrillarin and GAR1. Fibrillarin and GAR1 are specific markers of the two classes of small nucleolar ribonucleoprotein particles (snoRNPs) that are involved in posttranscriptional processing and modification of ribosomal RNA. SMN interaction requires the arginine- and glycine-rich domains of both fibrillarin and GAR1 and is defective in SMN mutants found in some SMA patients. Coimmunoprecipitations demonstrate that the SMN complex associates with fibrillarin and with GAR1 in vivo. The inhibition of RNA polymerase I transcription causes a transient redistribution of SMN to the nucleolar periphery and loss of fibrillarin and GAR1 colocalization with SMN in gems. Furthermore, the expression of a dominant-negative mutant of SMN (SMNDeltaN27) causes snoRNPs to accumulate outside of the nucleolus in structures that also contain components of gems and coiled (Cajal) bodies.


CONCLUSIONS
These findings identify fibrillarin and GAR1 as novel interactors of SMN and suggest a function for the SMN complex in the assembly and metabolism of snoRNPs. We propose that the SMN complex performs functions necessary for the biogenesis and function of diverse ribonucleoprotein complexes.
Pellizzoni
L
L
Howard Hughes Medical Institute and Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
Baccon
J
J
Charroux
B
B
Dreyfuss
G
G
D001120:Arginine / Q000737:chemistry; D001665:Binding Sites; D002466:Cell Nucleolus / Q000378:metabolism; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D017124:Conserved Sequence; D017362:Cyclic AMP Response Element-Binding Protein; D005998:Glycine / Q000737:chemistry; D006367:HeLa Cells; D006801:Humans; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020718:Ribonucleoproteins, Small Nucleolar / Q000378:metabolism*; D055532:SMN Complex Proteins; D014158:Transcription, Genetic
D002868:Chromosomal Proteins, Non-Histone; D017362:Cyclic AMP Response Element-Binding Protein; C485802:GAR1 protein, human; C407731:GAR1 protein, mammalian; D009419:Nerve Tissue Proteins; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D020718:Ribonucleoproteins, Small Nucleolar; D055532:SMN Complex Proteins; C047458:fibrillarin; D001120:Arginine; D005998:Glycine