Copy Number Control in the <i>Tetrahymena</i> Macronuclear Genome

Larson, Drena D.; Umthun, Angela R.; Shaiu, Wen‐Ling

doi:10.1111/j.1550-7408.1991.tb04439.x

Cited by 34 publications

(29 citation statements)

References 54 publications

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“…Ciliophora is perhaps the most morphologically differentiated taxon among protists (Fleury et al 1992;Larson et al 1991;Lynn 2008), and the genomic organization of ciliates is unique among eukaryotes (Prescott 1994). Zufall et al (2006) compared the evolutionary rates of 6 genes (Actin, ␣-, ␤-Tubulin, EF1␣, Histone H4, and HSP90) of ciliates with animals and fungi, and proposed that genome architecture, including nuclear dimorphism and chromosome fragmentation, leads to elevated rates of protein evolution in ciliates.…”

Section: Introductionmentioning

confidence: 99%

Variations and evolution of polyubiquitin genes from ciliates

Liu

Shi

Gong

2013

European Journal of Protistology

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Polyubiquitin genes from seven ciliate species were amplified, cloned and sequenced. It is estimated that Strombidium sulcatum, Euplotes vannus, E. rariseta and Anteholosticha manca have a polyubiquitin gene of 3 repeats, and A. parawarreni, Paramecium caudatum and Pseudokeronopsis flava 4 repeats. The newly obtained ubiquitins mostly differ from that of humans by 1-5 residues in amino acid sequences. A neighbor-joining tree constructed based on monomeric ubiquitin genes supports the monophyly of an assemblage comprising the litostomateans and some oligohymenophoreans, but not the class Spirotrichea. The monomers from the same species are generally placed together and highly supported for the class Litostomatea, the genera Paramecium and Ichthyophthirius, but not for other species. The non-synonymous/synonymous rate ratio (dN/dS) at the protein level are less than 1, and the synonymous nucleotide differences per synonymous site (p S ) from intraspecific comparisons are fairly high (0.02-0.72). These results indicate that ciliates have not only the conserved, but also some quite divergent, polyubiquitin genes and confirm that the polyubiquitin genes in ciliates evolve according to the birth-and-death mode of evolution under strong purifying selection.

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Section: Introductionmentioning

confidence: 99%

Variations and evolution of polyubiquitin genes from ciliates

Liu

Shi

Gong

2013

European Journal of Protistology

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“…The subtle effects of the rmm3 promoter region mutation on rDNA minichromosome maintenance in competition with another rDNA allele were detectable because macronuclear division is amitotic and chromosomes do not segregate faithfully and because copy number control requires some abrogation of cell cycle control in the macronucleus (28,41). Thus, the unusual features of the Tetrahymena macronucleus have allowed us to uncover an interplay between the promoter region and upstream nonnucleosomal regions of the rDNA minichromosome.…”

Section: Discussionmentioning

confidence: 92%

“…The increased accumulation of replicating intermediates in the 5Ј NTS of rmm3 cells indicates that at least one defect in rmm3 rDNA maintenance is at the level of replication elongation. This defect alone would affect rDNA minichromosome maintenance as a result of a combination of factors: copy number control of the rDNA minichromosome, the apparent abrogation of cell cycle control in the macronucleus, and the absence of a mechanism to ensure faithful segregation of replicated alleles (28,41). Thus, a slowly replicating rDNA allele could be gradually displaced in the macronucleus by one which replicated more quickly, with eventual loss of the mutant allele.…”

Section: Discussionmentioning

confidence: 99%

“…1A). This molecule is amplified to approximately 10 4 copies in the developing macronucleus and is maintained at this copy number during subsequent cell divisions (18,20,21,28).…”

mentioning

confidence: 99%

“…Strikingly, the base change in each of these rDNA minichromosome maintenance mutants is a deletion of an A residue in the central run of 11 A's in a type I sequence element. While minichromosome maintenance must entail replication, segregation, and copy number control (27,28), the proximity of the upstream maintenance mutant base changes (rmm1 and rmm4) to the mapped replication origin suggested that these base changes affect rDNA minichromosome replication (21,27).…”

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confidence: 99%

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A Promoter Region Mutation Affecting Replication of the Tetrahymena Ribosomal DNA Minichromosome

Gallagher

Blackburn

1998

Molecular and Cellular Biology

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In the ciliated protozoan Tetrahymena thermophila the ribosomal DNA (rDNA) minichromosome replicates partially under cell cycle control and is also subject to a copy number control mechanism. The relationship between rDNA replication and rRNA gene transcription was investigated by the analysis of replication, transcription, and DNA-protein interactions in a mutant rDNA, the rmm3 rDNA. The rmm3 (for rDNA maturation or maintenance mutant 3) rDNA contains a single-base deletion in the rRNA promoter region, in a phylogenetically conserved sequence element that is repeated in the replication origin region of the rDNA minichromosome. The multicopy rmm3 rDNA minichromosome has a maintenance defect in the presence of a competing rDNA allele in heterozygous cells. No difference in the level of rRNA transcription was found between wild-type and rmm3 strains. However, rmm3 rDNA replicating intermediates exhibited an enhanced pause in the region of the replication origin, roughly 750 bp upstream from the rmm3 mutation. In footprinting of isolated nuclei, the rmm3 rDNA lacked the wild-type dimethyl sulfate (DMS) footprint in the promoter region adjacent to the base change. In addition, a DMS footprint in the origin region was lost in the rmm3 rDNA minichromosome. This is the first reported correlation in this system between an rDNA minichromosome maintenance defect and an altered footprint in the origin region. Our results suggest that a promoter region mutation can affect replication without detectably affecting transcription. We propose a model in which interactions between promoter and origin region complexes facilitate replication and maintenance of the Tetrahymena rDNA minichromosome.

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Developmental analysis of the cell recognition mechanism in the ciliate Euplotes raikovi

et al. 1992

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Euplotes raikovi, like other ciliates, passes through a postconjugal immaturity, operatively identified by an apparent cell inability to form mating pairs under experimental conditions that are the same as those used for inducing mating at maturity. In cells homozygous for the gene mat-2, which controls the pheromone Er-2, Er-2 mRNA synthesis and mature Er-2 secretion were shown to start from the very beginning of the life cycle and continue throughout immaturity, although to extents estimated to be 5- to 10-fold lower than at maturity. In addition, experiments of 125I-Er-2 binding and crosslinking provided evidence that autocrine pheromone-binding sites, showing values of the dissociation constant of the order of 10(-9) M, are on the surface of immature cells. The number of these sites per cell was estimated to increase from less than 10(6) per cell of 5-7 fissions of age, to about 16 x 10(6) at maturity. These results were taken to suggest that a pheromone-receptor production is stimulated during immaturity by autocrine pheromone binding to cells and that this production might be essential for the development of a pheromone-receptor density high enough to transform the cell from "immature" to "adult," that is competent to respond as well to pheromones of conspecific, genetically different cells.

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Copy Number Control in the Tetrahymena Macronuclear Genome

Cited by 34 publications

References 54 publications

Variations and evolution of polyubiquitin genes from ciliates

Variations and evolution of polyubiquitin genes from ciliates

A Promoter Region Mutation Affecting Replication of the Tetrahymena Ribosomal DNA Minichromosome

Developmental analysis of the cell recognition mechanism in the ciliate Euplotes raikovi

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