Molecular Reorganization During Nuclear Differentiation in Ciliates

Steinbrück, Günther

doi:10.1007/978-3-540-39838-7_3

Cited by 34 publications

(6 citation statements)

References 138 publications

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“…In addition, all of these organisms show an unusual macronuclear DNA replication process involving "replication bands." The hypotrich mode of macronuclear development has generally been viewed as the most highly evolved and specialized, while organisms that produce larger macronuclear molecules and eliminate less DNA (e.g., Tetrahymena, Paramecium) are considered as precursors to the hypotrich mode (31).…”

Section: Resultsmentioning

confidence: 99%

Differential use of termination codons in ciliated protozoa.

Harper

Jahn

1989

Proc. Natl. Acad. Sci. U.S.A.

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Sequence analysis of genes in four species of ciliated protozoa and analysis of tRNAs in Tetrahymena has demonstrated that TAG and TAA encode glutamine or glutamic acid in these organisms and TGA is the only stop codon. Thus, it has generally been assumed that all ciliates use a nonuniversal genetic code in which TGA acts as the sole termination codon. We have sequenced the linear DNA molecules that carry an actin gene and a P-tubulin gene from the ciliate Euplotes crassus. These genes are shown to use TAA as a termination codon based on homology to known actin and ,-tubulin gene sequences. In addition, we have sequenced a portion of the 3' terminus of the E. crassus H4 histone gene and show that it also uses TAA as a termination codon. These data indicate that the timing of genetic code changes in the ciliates must be reconsidered.Ciliated protozoa are characterized by the possession of two types of nuclei: a germ-line micronucleus, which is transcriptionally inactive, and a vegetative macronucleus, which is responsible for most, if not all, transcription in the cell. Hypotrichous ciliates such as Euplotes, Stylonychia, and Oxytricha undergo a macronuclear developmental process that involves the degradation of >90% of all micronuclear DNA sequences and amplification of the remaining macronuclear-destined sequences (for review see ref. 1). These macronuclear molecules range in size from 400 base pairs (bp) to 20 kilobase pairs (kb) and are present in thousands of copies. Each molecule is believed to encode a single gene product and to contain all the information necessary for its replication and transcription. Holotrichous ciliates, such as Tetrahymena, undergo a similar, but less drastic, process of macronuclear development, in which 10-20% of all micronuclear sequences are degraded (2), and the resulting macronuclear molecules average 600 kb in size (3). Amplification of macronuclear sequences also occurs in Tetrahymena, resulting in -45 copies of each macronuclear chromosome (3).All ciliate macronuclear genes sequenced to date use TGA as a stop codon (4). A number of these genes appear to use TAA and TAG as glutamine or glutamic acid codons at internal positions in the gene. A comparison of the derived amino acid sequence of Stylonychia lemnae a-tubulin with other known a-tubulins showed that a single TAA codon in the Stylonychia gene corresponded to glutamine (5). In addition, actin and two different H3 histone genes in Tetrahymena thermophila appear to use TAA as a glutamine codon (6-8), and two surface antigen genes in Paramecium contain both TAA and TAG codons that specify either glutamine or glutamic acid (9, 10). Both a TAA and a TAG codon are internal to an open reading frame that shares significant homology with ADP/ATP carrier proteins from other organisms and is found on an alternatively processed family of macronuclear chromosomes in Oxytricha fallax (11). Recent experiments have shown that T. thermophila possesses tRNAs with anticodons specific for TAA and TAG codons that are aminoacylated...

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Section: Resultsmentioning

confidence: 99%

Differential use of termination codons in ciliated protozoa.

Harper

Jahn

1989

Proc. Natl. Acad. Sci. U.S.A.

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“…The macronucleus contains DNA on sub-chromosomal fragments, which in Paramecium and Tetrahymena range from 50 kb to more than 1,500 kb [ 1 , 5 ]. Macronuclei are generated from the post conjugation micronuclei in a complex process that involves DNA elimination and large-scale genomic rearrangements [ 5 - 10 ]. This process and the genetic organization of the macronucleus have been intensively studied in both peritrichous and spirotrichous (formerly hypotrichous) ciliates [ 5 , 7 , 8 , 11 ].…”

Section: Introductionmentioning

confidence: 99%

“…In certain spirotrichous ciliates, the development of the new macronucleus involves transient formation of polytene chromosomes [ 6 , 10 ]. These giant chromosomes resemble the polytene chromosomes of dipteran larvae but are transcriptionally inactive and disintegrate shortly after reaching their highest degree of polyteny [ 6 , 10 ]. Genome rearrangements, DNA elimination and, lastly, reorganization of the residual DNA into "gene-sized pieces" occur during the breakdown of polytene chromosomes.…”

Section: Introductionmentioning

confidence: 99%

“…There are some reports [ 17 - 20 ] that the heterotrichous ciliates Nyctotherus cordiformis and N. ovalis , which live in the intestinal tracts of frogs and cockroaches, respectively, form polytene chromosomes after conjugation, similar to Stylonychia [ 21 ]. With respect to the structure of the N. ovalis macronuclear chromosomes there is evidence from studies on individual genes, such as those for hydrogenase [ 10 ] and alpha tubulin [ 22 ] from telomere-capped sequences [ 16 ], as well as from a set of 34 complete macronuclear chromosomes [ 23 ], that N. ovalis , like Stylonychia , has gene-sized chromosomes. Alignment of the macronuclear chromosomes with known proteins furthermore has indicated the presence of short (< 30 nt) introns [ 15 , 16 , 22 , 23 ].…”

Section: Introductionmentioning

confidence: 99%

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Macronuclear genome structure of the ciliate Nyctotherus ovalis: Single-gene chromosomes and tiny introns

et al. 2008

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Background: Nyctotherus ovalis is a single-celled eukaryote that has hydrogen-producing mitochondria and lives in the hindgut of cockroaches. Like all members of the ciliate taxon, it has two types of nuclei, a micronucleus and a macronucleus. N. ovalis generates its macronuclear chromosomes by forming polytene chromosomes that subsequently develop into macronuclear chromosomes by DNA elimination and rearrangement.

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“…T have been ofexperimental interest for a number ofreasons, most notably the extreme genome reorganization process that occurs during their life cycle (for reviews see: 13,26). Following conjugation or mating, these organisms transform a mitotic copy of their chromosomal micronucleus into a transcriptionally active and DNA-rich macronucleus that contains only linear, genesized DNA molecules.…”

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confidence: 99%

Genetic Characterization and Use of a Restriction Fragment Length Variant in the Hypotrichous Ciliate Euplotes crassus¹

Baird

Klobutcher

1988

The Journal of Protozoology

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Two forms of a macronuclear DNA molecule differing in the presence or absence of a restriction endonuclease recognition site have been detected in the hypotrichous ciliate Euplotes crassus. Through a series of genetic crosses the two forms were shown to be allelic, being derived from a single micronuclear genetic locus. This restriction fragment length variant (RFLV) was used as a genetic marker to determine that the migratory and stationary pronuclei generated during mating can be genetically non-identical. In addition, the RFLV was used to investigate the efficiency of processing of the alternate alleles during macronuclear development and their subsequent transmission during vegetative growth. Little or no bias in the processing and/or amplification of the two alleles was observed during macronuclear development. During vegetative growth, however, changes in the relative amounts of the two alleles were observed.

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Molecular Reorganization During Nuclear Differentiation in Ciliates

Cited by 34 publications

References 138 publications

Differential use of termination codons in ciliated protozoa.

Differential use of termination codons in ciliated protozoa.

Macronuclear genome structure of the ciliate Nyctotherus ovalis: Single-gene chromosomes and tiny introns

Genetic Characterization and Use of a Restriction Fragment Length Variant in the Hypotrichous Ciliate Euplotes crassus¹

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Molecular Reorganization During Nuclear Differentiation in Ciliates

Cited by 34 publications

References 138 publications

Differential use of termination codons in ciliated protozoa.

Differential use of termination codons in ciliated protozoa.

Macronuclear genome structure of the ciliate Nyctotherus ovalis: Single-gene chromosomes and tiny introns

Genetic Characterization and Use of a Restriction Fragment Length Variant in the Hypotrichous Ciliate Euplotes crassus1

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Genetic Characterization and Use of a Restriction Fragment Length Variant in the Hypotrichous Ciliate Euplotes crassus¹