Fibrillarin is a component of a nucleolar small nuclear ribonucleoprotein (SnRNP), functioning in vivo in ribosomal RNA processing [ (PUBMED:2026646) (PUBMED:8493104) ]. It is associated with U3, U8 and U13 small nuclear RNAs in mammals [ (PUBMED:2026646) ] and is similar to the yeast NOP1 protein [ (PUBMED:2686980) ]. Fibrillarin has a well conserved sequence of around 320 amino acids, and contains 3 domains, an N-terminal Gly/Arg-rich region; a central domain resembling other RNA-binding proteins and containing an RNP-2-like consensus sequence; and a C-terminal alpha-helical domain. An evolutionarily related pre-rRNA processing protein, which lacks the Gly/Arg-rich domain, has been found in various archaebacteria.
The survival of motor neurons (SMN) protein interacts with the snoRNP proteinsfibrillarin and GAR1.
Curr Biol. 2001; 11: 1079-88
Display abstract
BACKGROUND: The survival of motor neurons (SMN) protein is the protein product ofthe spinal muscular atrophy (SMA) disease gene. SMN and its associated proteinsGemin2, Gemin3, and Gemin4 form a large complex that plays a role in snRNPassembly, pre-mRNA splicing, and transcription. The functions of SMN in theseprocesses are mediated by a direct interaction of SMN with components of thesemachineries, such as Sm proteins and RNA helicase A. RESULTS: We show that SMNbinds directly to fibrillarin and GAR1. Fibrillarin and GAR1 are specific markersof 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 bothfibrillarin and GAR1 and is defective in SMN mutants found in some SMA patients. Coimmunoprecipitations demonstrate that the SMN complex associates withfibrillarin and with GAR1 in vivo. The inhibition of RNA polymerase Itranscription causes a transient redistribution of SMN to the nucleolar peripheryand 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 componentsof gems and coiled (Cajal) bodies. CONCLUSIONS: These findings identifyfibrillarin and GAR1 as novel interactors of SMN and suggest a function for theSMN complex in the assembly and metabolism of snoRNPs. We propose that the SMNcomplex performs functions necessary for the biogenesis and function of diverseribonucleoprotein complexes.
