Table 1. The F2 USE specifically interacts with splicing factors, 3′ end processing proteins and other RNA binding proteins
Characteristics of USE‐binding proteinsAccession numberScore maxPeptidesImmunoblot
Splicing factors
 PSF/SFPQSplicing factor, proline and glutamine richP2324654715USE=Unrel.
 p54nrb/NonONon‐POU domain‐containing octamer‐binding proteinQ1523341415USE<Unrel.
 hnRNPI/PTBPolypyrimidine tract‐binding protein 1P265992628USE
 DHX 15Putative pre‐mRNA splicing factor RNA helicase (DEAH box protein 15)O431431907USE=Unrel.
 TDP43TAR DNA‐binding protein 43Q131481613USE=Unrel.
 DDX5 p68Probable RNA‐dependent helicase p68 (DEAD/H box 5)P17844842Very weak
 SF1Splicing factor 1 (zinc‐finger protein 162) (transcription factor ZFM1)Q15637785Not detectable
 U2AF65Splicing factor U2AF 65‐kDa subunitP26368742USE
 U2AF35Splicing factor U2AF 35‐kDa subunitQ01081501USE
 SF3BSplicing factor 3B subunit 3Q15393362Not determined
3End processing
 CstF 50Cleavage stimulation factor, 50‐kDa subunitQ050481828USE
 CPSF 160Cleavage and polyadenylation specificity factor, 160‐kDa subunitQ105701688USE
 CstF 77Cleavage stimulation factor subunit 3gi∣45574951346USE
 CstF 64Cleavage stimulation factor, 64‐kDa subunitP332401023USE
 CPSF 100Cleavage and polyadenylation specificity factor, 100‐kDa subunitQ9P2I0893USE
 Similar to Raver1?Unknown (protein for IMAGE:5113697)gi∣22902182912USE
 hnRNP C1/C2Heterogeneous nuclear ribonucleoproteins C1/C2P07910832USE=USEmut=Unrel.
 hnRNP A2/B1Heterogeneous nuclear ribonucleoproteins A2/B1P22626502Not detectable
 Nuclear DNA helicase IIATP‐dependent RNA helicase AQ08211432Not determined
  • USE‐binding proteins identified by affinity purification and subsequent mass spectrometry of USE‐specific bands shown in Figure 4A. The analysis also revealed the presence of ATP citrate synthase, LRP 130, HSP 90‐alpha and tubulin (Figure 4A, lane 1, black asterisks), which were judged to represent likely contaminants and were not included in the table. Data interpretation was performed with the MASCOT V2.1 search engine for mass spectrometric data (see Materials and methods section). The maximal scores obtained for each individual protein and the number of aligned peptides are shown. The immunoblot data shown in Figure 4B are summarized.