Disease relevance of SNRPA

• We demonstrate that the DExH protein NPH-II from vaccinia virus can displace the protein U1A from RNA in an active adenosine triphosphate-dependent fashion [1].
• Experiments with a mixture of recombinant phage displaying U1A or the closely related protein U2B" demonstrated that addition of a competitor RNA can suppress selection of a protein with a higher affinity for a given RNA target, thereby allowing the preferential amplification of a lower affinity protein [2].
• A subset of lupus patients with severe nephritis and anti-nRNP reactivity produces autoantibodies primarily against two major epitopes of the nRNP A (also known as U1A) protein [3].
• The U1A domain responsible for binding to U1 small nuclear RNA was locally mutagenized and displayed as a combinatorial library on filamentous bacteriophage [4].
• Using hairpin II of U1 small nuclear RNA (U1hpII) or the 3' stem loop of histone mRNA as bait, we could selectively amplify T7 phage that display either the spliceosomal protein U1A or the histone stem loop-binding protein from a lung cDNA phage library containing more than 10(7) independent clones [2].

High impact information on SNRPA

• The possibility that this interaction may reflect a broader role of the U1A protein in polyadenylation is discussed [5].
• The human U1 snRNP-specific U1A protein autoregulates its production by binding its own pre-mRNA and inhibiting polyadenylation [5].
• The human U1A snRNP protein regulates polyadenylation via a direct interaction with poly(A) polymerase [5].
• Overexpression of human U1A protein in mouse cells results in down-regulation of endogenous mouse U1A mRNA accumulation [6].
• Unlike its close homologue the U1A protein, U2B" binds to its cognate RNA only in the presence of U2A', which contains leucine-rich repeats in its sequence [7].

Biological context of SNRPA

• The NMR structure of the 38 kDa U1A protein - PIE RNA complex reveals the basis of cooperativity in regulation of polyadenylation by human U1A protein [8].
• Poly(A) tail regulation requires cooperative binding of two human U1A proteins to an RNA regulatory region called the polyadenylation inhibition element (PIE) [8].
• The crystal structure of the RNA binding domain of the U1 small nuclear ribonucleoprotein A, which forms part of the ribonucleoprotein complex involved in the excision of introns, has been solved [9].
• Here we investigate nuclear import of U1A and U2B" in vitro and demonstrate that it occurs by an active, saturable process [10].
• U1A dimerization requires two separate regions, both located in the N-terminal 115 residues [11].

Anatomical context of SNRPA

• An ATP-dependent, Ran-independent mechanism for nuclear import of the U1A and U2B" spliceosome proteins [10].
• In order to further our studies on this complex and to determine the rest of the components of the SF-A complex, we prepared several stable HeLa cell lines that overexpress a tandem-affinity-purification-tagged version of U1A (TAP-tagged U1A) [12].
• After the stimulation for these samples with the soluble recombinant U1-small nuclear ribonucleoprotein A protein, proliferative T cell responses were observed [13].
• We have examined the fate of the immune response against a nuclear autoantigen using human U1 small nuclear ribonucleoprotein-A protein (HuA) transgenic (Tg) mice by adoptive transfer of autoreactive lymphocytes [14].
• Addition of purified MS2 coat protein or U1A caused a specific, dose-dependent repression of CAT biosynthesis in rabbit reticulocyte and wheat germ in vitro translation systems [15].

Associations of SNRPA with chemical compounds

• Since helix C undergoes a conformational change upon RNA binding, the structure shows that binding cooperativity and interactions with PAP occur only when U1A is bound to its cognate RNA [8].
• Adenosine triphosphate is capable of supporting U1A and U2B" import, whereas neither nonhydrolyzable adenosine triphosphate analogues nor GTP can do so [10].
• 13C NMR relaxation studies of RNA base and ribose nuclei reveal a complex pattern of motions in the RNA binding site for human U1A protein [16].
• However, the proline-rich region of U1-A, absent in U2-B", is encoded by a single exon, suggesting a specific function for this domain of U1-A [17].
• In this study, autoantibody recognition of native U1 snRNPs was investigated by dissociating the particle into four components (U1-70K, U1-A, U1-C, and the Sm core particle) using 1 M MgCl2 or ribonuclease treatment [18].

Physical interactions of SNRPA

• The NMR structure of the 38 kDa complex formed between two U1A molecules and PIE RNA shows that binding cooperativity depends on helix C located at the end of the RNA-binding domain and just adjacent to the PAP-interacting domain of U1A [8].
• Here we examined the effect of randomizing amino acids in the heavy chain complementarity determining region 3 (CDR3) of this germline encoded recombinant antibody fragment on binding to the U1A protein [19].

Other interactions of SNRPA

• When bound to PIE RNA, U1A proteins also bind to the enzyme responsible for formation of the mature 3'-end of most eukaryotic mRNAs, poly(A) polymerase (PAP) [8].
• Fourteen residues of the U1 snRNP-specific U1A protein are required for homodimerization, cooperative RNA binding, and inhibition of polyadenylation [11].
• No association was found between DPB1 alleles and antibodies reacting with U1A and SmD1 antigens [20].
• We have previously shown that autoantigen-reactive T cells (CD4+) to U1-small nuclear ribonucleoprotein A were found in the PBMC of patients with systemic lupus erythematosus or mixed connective tissue disease [13].

Analytical, diagnostic and therapeutic context of SNRPA

• Using both coselection and gel mobility shift assays, U1A dimerization was also observed in vitro and found to depend on the same two regions that were found in vivo [11].
• Antibodies against U1A (tested in Western immunoblotting with HeLa cell extracts) were positively associated to DRB1*06 allele; antibodies reacting with SmD1 peptide 44-67 were negatively associated to DRB1*02 and DQB1*0602 alleles [20].
• We have now used GST fusion protein experiments, coimmunoprecipitations and Far Western blot analyses to demonstrate direct binding between U1A and the 160-kD subunit of cleavage-polyadenylation specificity factor (CPSF) [21].
• We report here that the rapidly formed intermediate of the spliceosomal protein U1A is an off-pathway artefact caused by transient aggregation of denatured protein under native conditions [22].
• T cell epitope mapping of U1-A RNP [23].

References