Cross-talk between snurportin1 subdomains.
The initial steps of spliceosomal small nuclear ribonucleoprotein (snRNP) maturation take place in the cytoplasm. After formation of an Sm-core and a trimethylguanosine (TMG) cap, the RNPs are transported into the nucleus via the import adaptor snurportin1 (SPN) and the import receptor importin-beta. To better understand this process, we identified SPN residues that are required to mediate interactions with TMG caps, importin-beta, and the export receptor, exportin1 (Xpo1/Crm1). Mutation of a single arginine residue within the importin-beta binding domain (IBB) disrupted the interaction with importin-beta, but preserved the ability of SPN to bind Xpo1 or TMG caps. Nuclear transport assays showed that this IBB mutant is deficient for snRNP import but that import can be rescued by addition of purified survival of motor neurons (SMN) protein complexes. Conserved tryptophan residues outside of the IBB are required for TMG binding. However, SPN can be imported into the nucleus without cargo. Interestingly, SPN targets to Cajal bodies when U2 but not U1 snRNPs are imported as cargo. SPN also relocalizes to Cajal bodies upon treatment with leptomycin B. Finally, we uncovered an interaction between the N- and C-terminal domains of SPN, suggesting an autoregulatory function similar to that of importin-alpha.
Ospina
Jason K
JK
Department of Genetics, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4955, USA.
Gonsalvez
Graydon B
GB
Bednenko
Janna
J
Darzynkiewicz
Edward
E
Gerace
Larry
L
Matera
A Gregory
AG
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D020541:Coiled Bodies / Q000378:metabolism; D017124:Conserved Sequence; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D028884:Karyopherins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009046:Motor Neurons / Q000378:metabolism; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D039381:RNA Cap-Binding Proteins / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D017413:Ribonucleoprotein, U2 Small Nuclear / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D028961:beta Karyopherins / Q000235:genetics / Q000378:metabolism*; D000097606:Exportin 1 Protein
D005231:Fatty Acids, Unsaturated; D028884:Karyopherins; D039381:RNA Cap-Binding Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D017413:Ribonucleoprotein, U2 Small Nuclear; D028961:beta Karyopherins; D000097606:Exportin 1 Protein; C114090:SNUPN protein, human; C038753:leptomycin B