Copyright@The McGraw-Hill Companies,Inc.Permission required for reproduction or display. Chapter 16 Other RNA Processing Events
Chapter 16 Other RNA Processing Events
16.1 Ribosomal RNA processing Eukaryotes .Structure of rRNA genes .The rRNA genes in eukaryotes are repeated several hundred times and clustered together in the nucleolus of the cell. .The rRNA genes are separated by regions called nontranscribed spacers (NTSs). ·rRNA processing .The trimming of excess regions from an RNA precursor is called processing. RNA processing similar to splicing,but it duffers from splicing in that no RNAs are stitched together during processing
16.1 Ribosomal RNA processing Eukaryotes •Structure of rRNA genes •The rRNA genes in eukaryotes are repeated several hundred times and clustered together in the nucleolus of the cell. •The rRNA genes are separated by regions called nontranscribed spacers (NTSs). •rRNA processing •The trimming of excess regions from an RNA precursor is called processing. • RNA processing similar to splicing, but it duffers from splicing in that no RNAs are stitched together during processing
The structure of rRNA gene Figure 16.1a rRNA gene NTS rRNA gene NTS Nontranscribed spacers
The structure of rRNA gene Nontranscribed spacers
Processing scheme of 45S human (HeLa)rRNA precursor rRNA gene RNA pol.I NTS 5 18S 5.8S 28S the 5'-end of the 45S precursor 45S RNA is removed→ Step1 441 S precursor▣ 18S 5.8S 28S is cut into two parts 41S Take place Step 2. in the 32S precursor 20S precursor nucleolus 18S ☐5.8S 28S 20S 32S 3'-end is removed Step 3. Step 4. cut 18S 5.8 28S rRNAs are made and the 5.8S and 28S rRNAs Step 5. associated by base pairing ribosome 5.8S Figure 16.2 M assembled 28S
rRNA gene Processing scheme of 45S human (HeLa) rRNA precursor RNA pol. I NTS Take place in the nucleolus rRNAs are made and ribosome assembled the 5.8S and 28S rRNAs associated by base pairing the 5'-end of the 45S precursor RNA is removed→ 32S precursor 3’-end is removed is cut into two parts 20S precursor 41S precursor cut
The evidence for this sequence of events a pulse-chase procedure to establish a precursor-product relationship between the 45S precursor and the 28S and 18S mature rRNAs Culture cell 3H]uridine short-lived Incubation with intermediate pulse-chase isotopes for a short time (pulse) 18S and 28S rRNAs increase Chase with 45S precursol decreased cold ubstrates The labeled RNA sedimented as a broad peak Collect samples centered at about 45S.Then he "chased"the label and detection at in this RNA into 18S and 28S rRNAs different time One or more RNA species was a precursor to 18S course. and 28S rRNAs
The evidence for this sequence of events a pulse-chase procedure to establish a precursor-product relationship between the 45S precursor and the 28S and 18S mature rRNAs. Culture cell Incubation with isotopes for a short time (pulse) Collect samples and detection at different time course. The labeled RNA sedimented as a broad peak centered at about 45S. Then he “chased" the label in this RNA into 18S and 28S rRNAs One or more RNA species was a precursor to 18S and 28S rRNAs Chase with cold ubstrates pulse-chase [ 3H]uridine 45S precursol decreased 18S and 28S rRNAs increased short-lived intermediates