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A block in mammalian splicing occurring after formation of large complexes containing U1, U2, U4, U5, and U6 small nuclear ribonucleoproteins. 1989

C H Agris, and M E Nemeroff, and R M Krug
Graduate Program of Molecular Biology, Memorial Sloan-Kettering Cancer Center, New York, New York 10021.

The assembly of mammalian pre-mRNAs into large 50S to 60S complexes, or spliceosomes, containing small nuclear ribonucleoproteins (snRNPs) leads to the production of splicing intermediates, 5' exon and lariat-3' exon, and the subsequent production of spliced products. Influenza virus NS1 mRNA, which encodes a virus-specific protein, is spliced in infected cells to form another viral mRNA (the NS2 mRNA), such that the ratio of unspliced to spliced mRNA is 10 to 1. NS1 mRNA was not detectably spliced in vitro with nuclear extracts from uninfected HeLa cells. Surprisingly, despite the almost total absence of splicing intermediates in the in vitro reaction, NS1 mRNA very efficiently formed ATP-dependent 55S complexes. The formation of 55S complexes with NS1 mRNA was compared with that obtained with an adenovirus pre-mRNA (pKT1 transcript) by using partially purified splicing fractions that restricted the splicing of the pKT1 transcript to the production of splicing intermediates. At RNA precursor levels that were considerably below saturation, approximately 10-fold more of the input NS1 mRNA than of the input pKT1 transcript formed 55S complexes at all time points examined. The pKT1 55S complexes contained splicing intermediates, whereas the NS1 55S complexes contained only precursor NS1 mRNA. Biotin-avidin affinity chromatography showed that the 55S complexes formed with either NS1 mRNA or the pKT1 transcript contained the U1, U2, U4, U5, and U6 snRNPs. Consequently, the formation of 55S complexes containing these five snRNPs was not sufficient for the catalysis of the first step of splicing, indicating that some additional step(s) needs to occur subsequent to this binding. These results indicate that the 5' splice site, 3' and branch point of NS1 and mRNA were capable of interacting with the five snRNPs to form 55S complexes, but apparently some other sequence element(s) in NS1 mRNA blocked the resolution of the 55S complexes that leads to the catalysis of splicing. On the basis of our results, we suggest mechanisms by which the splicing of NS1 is controlled in infected cells.

UI MeSH Term Description Entries
D007700 Kinetics The rate dynamics in chemical or physical systems.
D009975 Orthomyxoviridae A family of RNA viruses causing INFLUENZA and other respiratory diseases. Orthomyxoviridae includes INFLUENZAVIRUS A; INFLUENZAVIRUS B; INFLUENZAVIRUS C; INFLUENZAVIRUS D; ISAVIRUS; and THOGOTOVIRUS. Influenza Viruses,Myxoviruses,Orthomyxoviruses,Influenza Virus,Myxovirus,Orthomyxovirus
D010957 Plasmids Extrachromosomal, usually CIRCULAR DNA molecules that are self-replicating and transferable from one organism to another. They are found in a variety of bacterial, archaeal, fungal, algal, and plant species. They are used in GENETIC ENGINEERING as CLONING VECTORS. Episomes,Episome,Plasmid
D002846 Chromatography, Affinity A chromatographic technique that utilizes the ability of biological molecules, often ANTIBODIES, to bind to certain ligands specifically and reversibly. It is used in protein biochemistry. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed) Chromatography, Bioaffinity,Immunochromatography,Affinity Chromatography,Bioaffinity Chromatography
D005091 Exons The parts of a transcript of a split GENE remaining after the INTRONS are removed. They are spliced together to become a MESSENGER RNA or other functional RNA. Mini-Exon,Exon,Mini Exon,Mini-Exons
D006367 HeLa Cells The first continuously cultured human malignant CELL LINE, derived from the cervical carcinoma of Henrietta Lacks. These cells are used for, among other things, VIRUS CULTIVATION and PRECLINICAL DRUG EVALUATION assays. Cell, HeLa,Cells, HeLa,HeLa Cell
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000256 Adenoviridae A family of non-enveloped viruses infecting mammals (MASTADENOVIRUS) and birds (AVIADENOVIRUS) or both (ATADENOVIRUS). Infections may be asymptomatic or result in a variety of diseases. Adenoviruses,Ichtadenovirus,Adenovirus,Ichtadenoviruses
D012261 Ribonucleoproteins Complexes of RNA-binding proteins with ribonucleic acids (RNA). Ribonucleoprotein
D012322 RNA Precursors RNA transcripts of the DNA that are in some unfinished stage of post-transcriptional processing (RNA PROCESSING, POST-TRANSCRIPTIONAL) required for function. RNA precursors may undergo several steps of RNA SPLICING during which the phosphodiester bonds at exon-intron boundaries are cleaved and the introns are excised. Consequently a new bond is formed between the ends of the exons. Resulting mature RNAs can then be used; for example, mature mRNA (RNA, MESSENGER) is used as a template for protein production. Precursor RNA,Primary RNA Transcript,RNA, Messenger, Precursors,RNA, Ribosomal, Precursors,RNA, Small Nuclear, Precursors,RNA, Transfer, Precursors,Pre-mRNA,Pre-rRNA,Pre-snRNA,Pre-tRNA,Primary Transcript, RNA,RNA Precursor,mRNA Precursor,rRNA Precursor,snRNA Precursor,tRNA Precursor,Pre mRNA,Pre rRNA,Pre snRNA,Pre tRNA,Precursor, RNA,Precursor, mRNA,Precursor, rRNA,Precursor, snRNA,Precursor, tRNA,Precursors, RNA,RNA Primary Transcript,RNA Transcript, Primary,RNA, Precursor,Transcript, Primary RNA,Transcript, RNA Primary

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