Eukaryotic rrna gene organization rRNA is synthesized in the nucleolus and assembled with proteins to form subunit the subunit is then transported into cytoplasm rDNA repeat unit ext ribosomal DNA repeating Ribosomal DNA repeating unit unIt Ribosomal DNA transcription unit 58S 18S rRNA rRNA gene 28s rRNA gene DNA NTS ETS ITS ETS Transcription b) Processing of pre-rRNA Transcription
Eukaryotic rRNA gene organization • rRNA is synthesized in the nucleolus and assembled with proteins to form subunit • the subunit is then transported into cytoplasm
rrNa processing in eukaryotes The precursor folds and complexes with proteins RNP as it is being transcribed in the nucleolus Many specific ribose methylations take place at over 100 sites and is carried out directly b by a subset of snRNP particles snrnps contain snrnas that have short streches of complementarity to parts of the rRNA and, by base pairing with it, they define where methylation takes place pre-rRNa processing is accompanied by the formation of 6os and 40s subunits
rRNA processing in eukaryotes • The precursor folds and complexes with proteins RNP as it is being transcribed in the nucleolus • Many specific ribose methylations take place at over 100 sites and is carried out directly by a subset of snRNP particles • snRNPs contain snRNAs that have short streches of complementarity to parts of the rRNA and, by base pairing with it, they define where methylation takes place • pre-rRNA processing is accompanied by the formation of 60S and 40S subunits
Processing of pre-TRNA Cleavage is by ribonucleases,核糖 N Processing of pre-rRNA Transcription 核酸酶,RNA酶 45S pre-rRNA 圈3 ·5.8 SrRNA iS H ETS bonded to 28S rrNa Cleavage in mature ribosome 41spre·rRNA 20S pre-rRNA 32S pre-rRNA folding H bonds 18S rRNA 5.8S rRNA 28S rRNA Hydrogen-bonded to28 s rRNA in画 mature ribosome 5.8S rRNA
Processing of pre-rRNA • Cleavage is by ribonucleases, 核糖 核酸酶, RNA酶 • 5.8S rRNA is Hbonded to 28S rRNA in mature ribosome
Introns in pre-rrNa gene Only a few organisms' rRNA gene has introns Splicing剪接 does not need protein, Ribozyme is a catalytic RNA molecules that catalyze particular biochemical reactions in the absence of protein Introns that does not need proteins for splicing are categorized as the group i intron In mrna, trna rrna genes in mitochondria and chloroplasts of yeast/fungi. In rRNA genes of all insects In rRNA genes. In some mRNA and RNA genes of bacteriophage
Introns in pre-rRNA gene • Only a few organisms’ rRNA gene has introns • Splicing剪接 does not need protein, Ribozyme is a catalytic RNA molecules that catalyze particular biochemical reactions in the absence of protein • Introns that does not need proteins for splicing are categorized as the group I intron • In mRNA, tRNA & rRNA genes in mitochondria and chloroplasts of yeast/fungi. In rRNA genes of all insects. In rRNA genes. In some mRNA and tRNA genes of bacteriophage
Self-splicing自我剪接 for the group I intron in trtrahymena pre-rrNA Tetrahymena pre-rRNA Cleavage and ligation are 408 nucleotides Exon 1 Intro Exon 2 two steps here 5多多A Cleavage at the 5 splice Cleavage at 5 splice junction and G addition junction, add g at the end 5- Exon 1 Intron Exon 2 圆3+5恒A 多3 Cleavage at the splice Cleavage at 3 splice junction Ligation of exons Release of intro Juntion Exon 1 Exon 2 Ligation of the exons Circularization Cleavage of the lariat intron of intron Lariat is an intermediate in RNA splicing in which a Cleavage of intron circular structure with a tail to give linear and circular pieces is created by a 5-2 bond
Self-splicing自我剪接 for the group I intron in trtrahymena pre-rRNA • Cleavage and ligation are two steps here • Cleavage at the 5’ splice junction, add G at the end • Cleavage at the 3’splice juntion • Ligation of the exons • Cleavage of the lariat intron • Lariat is an intermediate in RNA splicing in which a circular structure with a tail is created by a 5′-2′ bond