Detailed transcription map of the extrachromosomal ribosomal RNA genes in Tetrahymena thermophila
| Autor: | Werner A. Eckert, Nanni Din, Jan Engberg, Walter Kaffenberger, Ronald E. Pearlman |
|---|---|
| Rok vydání: | 1980 |
| Předmět: |
Base Composition
biology Transcription Genetic EcoRI Tetrahymena Extrachromosomal Inheritance Nucleic Acid Hybridization DNA DNA Restriction Enzymes Ribosomal RNA biology.organism_classification Molecular biology Restriction fragment Molecular Weight Microscopy Electron Genes Structural Biology RNA Ribosomal Extrachromosomal DNA biology.protein Coding region Internal transcribed spacer Molecular Biology Ribosomal DNA |
| Zdroj: | Journal of molecular biology. 142(3) |
| ISSN: | 0022-2836 |
| Popis: | A detailed transcription map of the free ribosomal RNA genes in Tetrahymena was constructed by physical mapping of the ribosomal DNA using restriction endonucleases ( Eco RI, Bam HI, Hind III, Pst I, Hae III, Msp I and Bgl II) combined with hybridization studies. These involved hybridization of purified intermediates in the rRNA maturation pathway to rDNA restriction fragments using the technique of Southern (1975) or the S 1 nuclease protection technique of Berk & Sharp (1977). The results obtained were confirmed by electron microscope mapping using the R-loop technique. The regions involved in transcription initiation and termination have been defined and it is shown that Tetrahymena exemplifies a case of a lower eukaryote in which the loss of transcribed spacer material during the processing of the pre-rRNA is very low (less than 20%). The largest stable transcription product ( M r = 2.0 × 10 6 to 2.3 × 10 6 ) contains the sequences for the mature, cytoplasmic 17 S and 26 S rRNA species with the 17 S closer to its 5′-terminal end. As reported recently, the 26 S coding region of rDNA contains an intervening sequence of about 400 base-pairs which is transcribed within the largest pre-rRNA molecules (Din et al. , 1979). The spliced pre-rRNA molecules are processed into nuclear precursors of 17 S and 26 S rRNA which map immediately adjacent to each other on the gene coding map. Very little, if any, cleavage processing takes place at the 3′-terminal end of the pre-rRNA molecules, while some processing resulting in a size reduction takes place at the 5′-terminal end during the steps leading to mature 26 S and 17 S rRNA, respectively. The distance between the regions coding for 17 S and 26 S rRNA is about 450 base-pairs and contains the region coding for the 26 S-associated 5.8 S rRNA within 100 bases of the 26 S rRNA gene in the transcribed spacer region. The nuclear precursor for 26 S rRNA ( M r = 1.4 × 10 6 ) contains sequences complementary to the 5.8 S coding region. The nuclear rRNA precursor found in fraction C ( M r = 0.96 × 10 6 ) previously suggested to be a precursor of the mature 17 S rRNA (Eckert et al. , 1978) is shown to derive from the 26 S rRNA precursor. The so-called “hidden break” in cytoplasmic 26 S rRNA, which results in the formation of two fragments F1 ( M r = 0.63 × 10 6 ) and F2 ( M r = 0.58 × 10 6 ) following denaturation of 26 S rRNA, could not be viewed by the R-loop technique but was mapped using the S 1 nuclease/alkaline agarose gel electrophoresis technique. |
| Databáze: | OpenAIRE |
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