第11章dna的復(fù)制、修復(fù)和重組-dnatranscr-資料下載頁
2025-03-04 13:34本頁面
【正文】 icing of PremRNA ? Splicing signals “internal cause” ? snRNPs “external cause” ? Splicing reaction two Transesterification reactions ? Assembly of spliceosomes Sequence requirements for splicing G 3’ Exon 5’ Exon AG GU AG Intron 18 40 nucleotides 3. Branch point YNYRAY Y= pyrimidine R= purine N = anything 1. 5’ splice site 2. 3’ splice site Splicing occurs through two Transesterification reactions P O O O O X Y RNA Chain + R OH P O O O O R Y X OH + ? In a transesterification reaction a phosphodiester bond is transferred to a different hydroxyl group ? There is no hydrolysis and no energy loss Alternative splicing Transsplicing Alternative splicing Splicing is precise BUT... ? Individual premRNA may be spliced to more than one kind of mRNA by removing different binations of introns/exons ? Alternative forms can be regulated Sex determination in Drosophila Transsplicing ? Definition 539。 and 339。 junctions on different RNA molecules ? Relatively rare otherwise ? Occurs naturally in trypanosomes and in C. elegans maybe elsewhere too. Alternative splicing can generate multiple proteins from a single gene Capping Tailing Posttranscriptional processing of prerRNA ? In karyotes Cleavage, trimming and modification ? In eukaryotes 1) Cleavage, trimming and modification 2) Splicing (Some eukaryotes such as Tetrahymena四膜蟲 ) Selfsplicing of PrerRNA ? Discovery (1989 Nobel Prize Laureate in Chemistry) found 26S rRNA has one 400 b intron in some Tetrahymena strains in 1981:This Intron can SelfSplice。 requires ions and a Gnuc (GTP, GDP, GMP, GR) and doesn’t require any proteins ? L19 RNA enzymatic activities 1) Nucleotidyl transferase or RNA polymerase 2) Endoribonuclease。 RNA ligase。 Phosphatase Intron Exon1 Exon2 Posttranscriptional processing of pre tRNA ? In Prokaryotes 1) Cleavage and trimming 2) Modification 3) Addition of CCA (if necessary) ? In eukaryotes 1) Cleavage and trimming 2) Modification 3) Addition of CCA 4) Splicing (some eukaryotes) RNase P A true ribozyme ? DiscovererSidney Altman (1989 Nobel Prize Laureate in Chemistry) ? Structure and Function 1) An endonuclease –involved in 5’end processing of pretRNA 2) E. coli RNase P: 14kDa polypeptide + a 377nucleotide RNA ( M1 RNA). 3) At high Mg2+ concentrations, isolated M1 RNA recognizes and cleaves E. coli pretRNAs. The RNase P polypeptide increases the rate of cleavage by M1 RNA, allowing it to proceed at physiological Mg2+ concentrations. RNAs that function as enzymes ? Types 1) RNase P 2) Group I introns ( Found in prerRNAs from some singlecelled anisms, in mitochondrial and chloroplast prerRNAs, in several premRNAs from certain E. coli bacteriophages, and in some bacterial tRNA primary transcripts ) 3) Group II introns (Found in certain mitochondrial and chloroplast premRNAs) 4) 23S rRNA: peptide bond formation 5) Hammerhead ribozymes (some plant viruses) 6) snRNAs involved in splicing ? Features ? Significance – “RNA world” Who was produced first, DNA or Protein？ RNA， RNA， RNA RNA， RNA， RNA， RNA RNA， RNA， RNA RNA， RNA， RNA RNA world DNA Protein Retrotranscription ? Discovery 196039。s: Howard Temin knew that retrovirus genomes were posed of RNA and observed that replication was inhibited by actinomycin D therefore he proposed the concept of reverse transcription ( Nobel prize awarded to Baltimore and Temin, 1975 ). 1970: Temin and David Baltimore (separately) discover the RNAdirected DNA polymerase reverse trascriptase ? Retroviruses Retrotranscriptase Three enzymatic activities: RDNAP, DNAP and RNase H ? cDNA See you next time! 演講完畢，謝謝觀看！
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