Despite the great sequence similarity between U1A and U2B", both proteins do have a difference in RNA binding specificity and in the way they bind to their cognate RNAs. The U1A protein is able to bind in vitro U1 RNA independently of other factors. The U2B" protein binds specifically to U2 RNA in the presence of the U2A' protein only. We have compared the effect on RNA binding of multiple doub...

In Caenorhabditis elegans, the small nuclear ribonucleoprotein (snRNP)-associated proteins U1A and U2B'' are approximately 50% identical to each other, and neither bears signature characteristics of mammalian U1A or U2B'' or the single Drosophila homolog, SNF. We show here that the genes that encode these proteins (rnp-2 and rnp-3) are cotranscribed in an operon, and that ribonucleoprotein RNP-...

Nuclear import of the two uracil-rich small nuclear ribonucleoprotein (U snRNP) components U1A and U2B" is mediated by unusually long and complex nuclear localization signals (NLSs). Here we investigate nuclear import of U1A and U2B" in vitro and demonstrate that it occurs by an active, saturable process. Several lines of evidence suggest that import of the two proteins occurs by an import mech...

Nuclear transport of the U1 snRNP-specific protein U1A has been examined. U1A moves to the nucleus by an active process which is independent of interaction with U1 snRNA. Nuclear localization requires an unusually large sequence element situated between amino acids 94 and 204 of the protein. U1A transport is not unidirectional. The protein shuttles between nucleus and cytoplasm. At equilibrium,...

In the vertebrate lineage of the U1A/U2B″/SNF protein family, the U1A and U2B″ proteins bind to RNA stem-loops in the U1 or U2 snRNPs, respectively. However, their specialization is fairly recent, as they evolved from a single ancestral protein. The progress of their specialization (subfunctionalization) can be monitored by the amino acid sequence changes that give rise to their modern RNA-bind...

DExH/D proteins catalyze NTP-driven rearrangements of RNA and RNA-protein complexes during most aspects of RNA metabolism. Although the vast majority of DExH/D proteins displays virtually no sequence-specificity when remodeling RNA complexes in vitro, the enzymes clearly distinguish between a large number of RNA and RNP complexes in a physiological context. It is unknown how this discrimination...

Molecular dynamics (MD) simulations on stem loop 2 of U1 small nuclear RNA and a construct of the U1A protein were carried out to obtain predictions of the structures for the unbound forms in solution and to elucidate dynamical aspects of induced fit upon binding. A crystal structure of the complex between the U1A protein and stem loop 2 RNA and an NMR structure for the uncomplexed form of the ...

In an enhancer screen for yeast mutants that may interact with U1 small nuclear RNA (snRNA), we identified a gene that encodes the apparent yeast homolog of the well-studied human U1A protein. Both in vitro and in vivo, the absence of the protein has a dramatic effect on the activity of U1 snRNP containing the mutant U1 snRNA used in the screen. Surprisingly, the U1A gene is inessential in a wi...

Autoantibodies against U small nuclear ribonucleoproteins (snRNP) are frequently present in the serum of patients with systemic rheumatic diseases, and have been reported to be associated with HLA-DR and -DQ genes. To better define the role of HLA genes in the production of such antibodies, we studied immunogenetic associations with autoantibodies reacting with U1 RNP, U1A and SmD1 proteins, an...

The N-terminal RNA Recognition Motif (RRM1) of the spliceosomal protein U1A interacting with its target U1 hairpin II (U1hpII) has been used as a paradigm for RRM-containing proteins interacting with their RNA targets. U1A binds to U1hpII via direct interactions with a 7-nucleotide (nt) consensus binding sequence at the 5' end of a 10-nt loop, and via hydrogen bonds with the closing C-G base pa...