Unusual ciliate-specific codons in <i>Tetrahymena</i> mRNAs are translated correctly in a rabbit reticulocyte lysate supplemented with a subcellular fraction from <i>Tetrahymena</i>

Andreasen, Per Hove; Dreisig, Hanne; Kristiansen, Karsten

doi:10.1042/bj2440331

Cited by 11 publications

(2 citation statements)

References 21 publications

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“…This is in contrast to results obtained using Tetrahymena (24) or Paramecium (25) mRNA in similar in vitro translation experiments, where only truncated proteins are produced. Addition of tRNAs from T. thermophila to the in vitro translation system restores the ability to produce full-length protein products (24). As previously discussed, T. thermophila possesses tRNAs that specifically recognize TAA and TAG and are aminoacylated with glutamine (12).…”

Section: Resultsmentioning

confidence: 81%

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: 81%

Differential use of termination codons in ciliated protozoa.

Harper

Jahn

1989

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

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“…In T. thermophila, TAA/G codes for glutamine (6,21,24,29,37). Therefore, the Tetrahymena HTA2 gene in pXL46 (32) was first mutagenized to change codon 28 from TAA Gln to CAA Gln by using Oligo 2285 (GCTGGTCTTCAAT TCCCCGTTGG) to give pXL84.…”

Section: Methodsmentioning

confidence: 99%

Either of the Major H2A Genes but Not an Evolutionarily Conserved H2A.F/Z Variant of Tetrahymena thermophila Can Function as the Sole H2A Gene in the Yeast Saccharomyces cerevisiae

Liu

Bowen

Gorovsky

1996

Molecular and Cellular Biology

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H2A.F/Z histones are conserved variants that diverged from major H2A proteins early in evolution, suggesting they perform an important function distinct from major H2A proteins. Antisera specific for hv1, the H2A.F/Z variant of the ciliated protozoan Tetrahymena thermophila, cross-react with proteins from Saccharomyces cerevisiae. However, no H2A.F/Z variant has been reported in this budding yeast species. We sought to distinguish among three explanations for these observations: (i) that S. cerevisiae has an undiscovered H2A.F/Z variant, (ii) that the major S. cerevisiae H2A proteins are functionally equivalent to H2A.F/Z variants, or (iii) that the conserved epitope is found on a non-H2A molecule. Repeated attempts to clone an S. cerevisiae hv1 homolog only resulted in the cloning of the known H2A genes yHTA1 and yHTA2. To test for functional relatedness, we attempted to rescue strains lacking the yeast H2A genes with either the Tetrahymena major H2A genes (tHTA1 or tHTA2) or the gene (tHTA3) encoding hv1. Although they differ considerably in sequence from the yeast H2A genes, the major Tetrahymena H2A genes can provide the essential functions of H2A in yeast cells, the first such case of trans-species complementation of histone function. The Tetrahymena H2A genes confer a cold-sensitive phenotype. Although expressed at high levels and transported to the nucleus, hv1 cannot replace yeast H2A proteins. Proteins from S. cerevisiae strains lacking yeast H2A genes fail to cross-react with anti-hv1 antibodies. These studies make it likely that S. cerevisiae differs from most other eukaryotes in that it does not have an H2A.F/Z homolog. A hypothesis is presented relating the absence of H2A.F/Z in S. cerevisiae to its function in other organisms.

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CLONING AND CHARACTERIZATION OF THE GENE ENCODING THE HIGHLY EXPRESSED RIBOSOMAL PROTEIN L3 OF THE CILIATED PROTOZOANTETRAHYMENA THERMOPHILA. EVIDENCE FOR DIFFERENTIAL CODON USAGE IN HIGHLY EXPRESSED GENES

Larsen¹,

Andreasen²,

Dreisig³

et al. 1999

Cell Biology International

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We have cloned and characterized the cDNA and the macronuclear genomic copy of the highly conserved ribosomal protein (r-protein) L3 of Tetrahymena thermophila. The r-protein L3 is encoded by a single copy gene interrupted by one intron. The organization of the promoter region exhibits features characteristic of ribosomal protein genes in Tetrahymena. The codon usage of the L3 gene is highly biased. A thorough analysis of codon usage in Tetrahymena genes revealed that genes could be categorized into two classes according to codon usage bias. Class A comprises r-protein genes and a number of other highly expressed genes. Class B comprises weakly expressed genes such as the conjugation induced CnjB and CnjC genes, but surprisingly, this class also contains abundantly expressed genes such as the genes encoding the surface antigens SerH3 and SerH1. Codon usage is slightly more restricted in class A than in class B, but both classes exhibit distinct and different codon usage biases. Class A genes preferentially use C and U in the silent third codon positions, whereas class B genes preferentially use A and U in the silent third codon positions. The analysis suggests that two different strategies have been employed for optimization of codon usage in the A+T-rich genome of Tetrahymena.

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Unusual ciliate-specific codons in Tetrahymena mRNAs are translated correctly in a rabbit reticulocyte lysate supplemented with a subcellular fraction from Tetrahymena

Cited by 11 publications

References 21 publications

Differential use of termination codons in ciliated protozoa.

Differential use of termination codons in ciliated protozoa.

Either of the Major H2A Genes but Not an Evolutionarily Conserved H2A.F/Z Variant of Tetrahymena thermophila Can Function as the Sole H2A Gene in the Yeast Saccharomyces cerevisiae

CLONING AND CHARACTERIZATION OF THE GENE ENCODING THE HIGHLY EXPRESSED RIBOSOMAL PROTEIN L3 OF THE CILIATED PROTOZOANTETRAHYMENA THERMOPHILA. EVIDENCE FOR DIFFERENTIAL CODON USAGE IN HIGHLY EXPRESSED GENES

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