Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.26.4 (RNase H)
 2,751 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have used protection against ribonuclease H to investigate the mechanisms by which U1 small nuclear ribonucleoprotein particles (snRNPs) determine the use of two alternative 5' splice sites. The initial binding of U1 snRNPs to alternative consensus splice sites was indiscriminate, and on a high proportion of pre-mRNA molecules both sites were occupied simultaneously. When the sites were close, this inhibited splicing. We propose that double occupancy leads to the use of the downstream site for splicing and that this is the cause of the proximity effect seen with strong alternative splice sites. This model predicts that splicing to an upstream site of any strength requires a low affinity of U1 snRNPs for the downstream site. This prediction was tested both by cleaving the 5' end of U1 snRNA and by altering the sequence of the downstream site of an adenovirus E1A gene. The enhancement of downstream 5' splice site use by splicing factor SF2/ASF appears to be mediated by an increase in the strength of U1 snRNP binding to all sites indiscriminately.
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PMID:Pathways for selection of 5' splice sites by U1 snRNPs and SF2/ASF. 825 84

Retroviruses use unspliced RNA as mRNA for expression of virion structural proteins and as genomic RNA; the full-length RNA often constitutes the majority of the viral RNA in an infected cell. Maintenance of this large pool of unspliced RNA is crucial since even a modest increase in splicing efficiency can lead to impaired replication. In Rous sarcoma virus, the negative regulator of splicing (NRS) was identified as a cis element that negatively impacts splicing of viral RNA. Components of the splicing apparatus appear to be involved in splicing inhibition since binding of a number of splicing factors (snRNPs and SR proteins) and assembly of a large complex (NRS-C) in nuclear extracts correlate with NRS-mediated splicing inhibition. In determining the requirements for NRS complex assembly, we show that NRS-C assembly can be reconstituted by addition of total SR proteins to an S100 extract that lacks these factors. Of the purified SR proteins tested, SF2/ASF was functional in NRS-C assembly, whereas SC35 and SRp40 were not. The participation of snRNPs in NRS-C assembly was addressed by selectively depleting individual snRNPs with oligonucleotides and RNase H or by sequestering critical snRNA domains with 2'-O-methyl RNA oligonucleotides. The results indicate that in addition to U11 snRNP, U1 snRNP and SR proteins, but not U2 snRNP, are involved in NRS-C assembly.
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PMID:SR protein and snRNP requirements for assembly of the Rous sarcoma virus negative regulator of splicing complex in vitro. 950 Oct 36