Free ribosomal RNA genes in the macronucleus of Tetrahymena.
نویسنده
چکیده
In the macronucleus of the ciliated protozoan, Tetrahymena pyriformis GL, the genes coding for 17S and 25S rRNA exist as free, extrachromosomal molecules. About 90% of the molecules are linear with a molecular weight of 12.6 x 10(6). Most of the remainder are circles of the same size, or lariats (circles with tails). A few dimers and oligomers are found. The extrachromosomal rDNA of Tetrahymena represents a kind of gene amplification that may be common among primitive eukaryotes.
منابع مشابه
Functional states of RNA polymerase in the macronucleus of Tetrahymena pyriformis and their dependence on culture growth.
RNA polymerase In in macronuclei of late log-phase cells of the ciliate Tetrahymena pyriformis is found to be present in 2 functional states, the one being actively engaged in transcription of ribosomal genes, the other one in a "free" state, i.e. free to transcribe added DNA or poly d(AT). Stimulation of RNA synthesis induced by dilution of stationary-phase cells into fresh medium is correlate...
متن کاملSequence organization within and flanking clusters of 5S ribosomal RNA genes in Tetrahymena.
Macro- and micronuclei of Tetrahymena thermophila each contain approximately 30 clusters of 5S genes per haploid genome. Structural changes in DNA sequences associated with some of these clusters occur during the development of the transcriptionally active macronucleus from the transcriptionally inert micronucleus. Exonuclease digestion indicates that DNA fragmentation is not responsible for th...
متن کاملA single integrated gene for ribosomal RNA in a eucaryote, Tetrahymena pyriformis.
The macronucleus of the protozoan, Tetrahymena, is known to contain multiple rRNA genes which are not linked to the chromosomes. Here we present evidence that the germinal micronucleus of this organism contains a single gene for rRNA integrated into the chromosomal DNA. Unlike the extrachromosomal copies of the macronucleus, which are composed of a pair of reversely repeated sequences (a palind...
متن کاملPreparation of chromatin containing ribosomal deoxyribonucleic acid from the macronucleus of Tetrahymena pyriformis.
A method is described that enables a chromatin fraction containing ribosomal DNA (DNA containing sequences coding for rRNA) to be prepared from the macronuclei of growing or stationary cultures of Tetrahymena pyriformis. This material is obtained in yields of between 25 and 75% of the theoretical maximum. The DNA in this fraction was identified as ribosomal DNA on the basis of its density and m...
متن کاملTetrahymena ribosomal RNA gene chromatin is digested by micrococcal nuclease at sites which have the same regular spacing on the DNA as corresponding sites in the bulk nuclear chromatin.
Synchronised cells of Tetrahymena pyriformis GL were labelled with 3H thymidine at a stage in the cell cycle when only the mitochondrial and extrachromosomal nucleolar ribosomal DNAs were replicating. In this way it was possible to prepare nuclei labelled selectively in the DNA of the ribosomal RNA genes. Since the ribosomal RNA cistrons of these cells are also very active in serving as a templ...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
- Proceedings of the National Academy of Sciences of the United States of America
دوره 71 8 شماره
صفحات -
تاریخ انتشار 1974