Disease relevance of snRNP70K

• A mutant transgene that lacks the PSI-U1 snRNP-interaction domain restores viability but shows courtship behavior abnormalities and meiosis defects during spermatogenesis, resulting in a complete male sterility phenotype [1].
• Here we describe for the first time the selection and characterization of recombinant human anti-U1-70K single chain autoantibody fragments (anti-hU1-70K scFv) from autoimmune patient-derived phage display antibody libraries [2].
• Some contain long repeats of Asp-Arg or Glu-Arg, among them the small nuclear ribonucleo-U1 70K protein, which is an autoantigen in systemic lupus erythematosis [3].

High impact information on snRNP70K

• By site-directed mutagenesis, we determined that the 70K protein consists of 437 amino acids (52 kd), and found that its aberrant electrophoretic migration is due to a carboxy-terminal charged domain structurally similar to two Drosophila proteins (su(wa) and tra) that may regulate alternative pre-messenger RNA splicing [4].
• The 5' flanking sequences of three distinct 70K genes were also determined [5].
• Here we summarize a study of the organization of genes coding for the 70K heat shock-specific protein contained in the two recombinant chromosomal DNA plasmids pG3 and pG5 [6].
• Here, we report that the conserved U1 snRNP-interacting RNA-binding protein PSI is essential for Drosophila viability [1].
• Direct interactions between RNA-binding proteins and snRNP particles modulate eukaryotic pre-mRNA processing patterns to control gene expression [1].

Biological context of snRNP70K

• We provide evidence that SEX-LETHAL interacts with SANS-FILLE in the context of the U1 snRNP, through the characterization of a point mutation that interferes with both assembly into the U1 snRNP and complex formation with SEX-LETHAL [7].
• Sex-lethal splicing autoregulation in vivo: interactions between SEX-LETHAL, the U1 snRNP and U2AF underlie male exon skipping [7].
• We have cloned snf and found that it has sequence homology to the mammalian U1A and U2B" snRNP proteins [8].
• The observation that increased snf(+) does not suppress other phenotypes associated with mutations that reduce U1-70k or SF3a(60) is additional evidence that snf(+) dose effects are not caused by increased snRNP levels [9].
• To better understand the relationship between hnRNP proteins and snRNP particles and their roles in mRNA formation, we have visualized them as they associate with nascent transcripts on the polytene chromosomes of Drosophila melanogaster salivary glands [10].

Anatomical context of snRNP70K

• Indeed, most of the reactive proteins observed in nuclear extract are detected in spliceosomes (E and/or B complex) assembled in vitro, including the U1 70K component of the U1 small nuclear ribonucleoprotein particle and both subunits of U2AF [11].

Associations of snRNP70K with chemical compounds

• Psoralen-mediated crosslinking experiments suggest that SXL binding to this uridine-rich sequence inhibits recognition of the 5' splice site by U1 snRNP in HeLa nuclear extracts [12].
• Velocity sedimentation in sucrose gradients was used to partially fractionate the RNPs; analysis of fractions so obtained suggests that, in general, one snRNP contains one snRNA [13].
• Our results are consistent with a role for the purine region in facilitated snRNP binding to the NRS via SF2/ASF [14].
• The Drosophila U1-70K protein is required for viability, but its arginine-rich domain is dispensable [15].

Physical interactions of snRNP70K

• The U1-70K protein is specifically bound to stemloop I of the U1 small nuclear RNA contained in the U1 small nuclear ribonucleoprotein complex (U1 snRNP), which is involved in the splicing of pre-mRNA [2].

Regulatory relationships of snRNP70K

• Both loss-of-function and gain-of-function mutations in snf define a role for snRNP proteins in regulating Sex-lethal pre-mRNA splicing in Drosophila development [16].

Other interactions of snRNP70K

• These data show that the processing of specific target transcripts, such as the P-element mRNA, is regulated by a functional PSI-U1 snRNP interaction in Drosophila [17].
• Its role, however, has remained enigmatic because of questions about whether SNF acts as part of an intact snRNP or a free protein [7].
• In contrast, increasing the dose of genes encoding either the integral U1 snRNP protein U1-70k, or the integral U2 snRNP protein SF3a(60), has no effect [9].
• Numerous differences in the relative amounts of snRNP particles and hnRNP proteins on nascent transcripts are also observed [10].
• Based on these studies we suggest a model in which the snRNP protein, Snf, functions with Sex-lethal to block recognition of the regulated male-specific exon [16].

Analytical, diagnostic and therapeutic context of snRNP70K

• Southern blot and in situ hybridizations showed that this U1 70K gene is unique in the Drosophila genome, residing at cytological position 27D1,2 [18].
• On the basis of R loop hybridization experiments and restriction enzyme analysis, we conclude that a 14 kb fragment, G3, contains three copies of the gene coding for the 70K protein [6].
• In Western blotting assays a number of scFv preferentially recognize the 40-kDa apoptotic cleavage fragment of the U1-70K protein, suggesting a possible involvement of this apoptotic cleavage product in the autoimmune response of patients [2].

References