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A micronucleus-specific sequence exists in the 5'-upstream region of calmodulin gene in Tetrahymena thermophila.

ABSTRACT: Tetrahymena thermophila possesses a transcriptionally inactive micronucleus and an active macronucleus. Both nuclei are developed from micronucleus-derived germ nuclei during conjugation. Extensive DNA rearrangement and transcriptional activation are known to be involved in macronuclear development, but little has been known about these processes in a particular functional gene. Therefore the micro- and macronuclear genomic DNAs for calmodulin gene were analyzed. A 1,384 bp micronucleus-specific sequence located about 3.5 kb upstream of calmodulin gene has been found, suggesting DNA rearrangement during macronuclear development. The micronucleus-specific sequence had 85% A + T, no extensive ORF, ATTAs at both ends, and two palindromic structures just outside of both ends. Interestingly, the micronucleus-specific sequence included a T-rich tract, T16CT5, in the middle, and a nearly complementary A-rich tract, A5TA10GA5, existed 7 bp upstream from the initiation codon. In addition, there was a 20 bp repetitive sequence TAAT(TAAC)4 about 100 bp upstream of the micronucleus-specific sequence and also in the promoter region of calmodulin gene. Although the functional significance of the micronucleus-specific sequence remains unclear, T16CT5 and TAAT(TAAC)4 elements might exert an influence on transcription of the calmodulin gene. Stringent Southern hybridization revealed that this micronucleus-specific sequence or very similar sequence(s) were abundant in the Tetrahymena micronuclear genome.

SUBMITTER: Katoh M

PROVIDER: S-EPMC309540 | biostudies-other | 1993 May

REPOSITORIES: biostudies-other

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A micronucleus-specific sequence exists in the 5'-upstream region of calmodulin gene in Tetrahymena thermophila.

Katoh M M Hirono M M Takemasa T T Kimura M M Watanabe Y Y

Nucleic acids research 19930501 10

Tetrahymena thermophila possesses a transcriptionally inactive micronucleus and an active macronucleus. Both nuclei are developed from micronucleus-derived germ nuclei during conjugation. Extensive DNA rearrangement and transcriptional activation are known to be involved in macronuclear development, but little has been known about these processes in a particular functional gene. Therefore the micro- and macronuclear genomic DNAs for calmodulin gene were analyzed. A 1,384 bp micronucleus-specific ...[more]

PMID: 8506136

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Project description:The ciliate Tetrahymena thermophila is a model organism for molecular and cellular biology. Like other ciliates, this species has separate germline and soma functions that are embodied by distinct nuclei within a single cell. The germline-like micronucleus (MIC) has its genome held in reserve for sexual reproduction. The soma-like macronucleus (MAC), which possesses a genome processed from that of the MIC, is the center of gene expression and does not directly contribute DNA to sexual progeny. We report here the shotgun sequencing, assembly, and analysis of the MAC genome of T. thermophila, which is approximately 104 Mb in length and composed of approximately 225 chromosomes. Overall, the gene set is robust, with more than 27,000 predicted protein-coding genes, 15,000 of which have strong matches to genes in other organisms. The functional diversity encoded by these genes is substantial and reflects the complexity of processes required for a free-living, predatory, single-celled organism. This is highlighted by the abundance of lineage-specific duplications of genes with predicted roles in sensing and responding to environmental conditions (e.g., kinases), using diverse resources (e.g., proteases and transporters), and generating structural complexity (e.g., kinesins and dyneins). In contrast to the other lineages of alveolates (apicomplexans and dinoflagellates), no compelling evidence could be found for plastid-derived genes in the genome. UGA, the only T. thermophila stop codon, is used in some genes to encode selenocysteine, thus making this organism the first known with the potential to translate all 64 codons in nuclear genes into amino acids. We present genomic evidence supporting the hypothesis that the excision of DNA from the MIC to generate the MAC specifically targets foreign DNA as a form of genome self-defense. The combination of the genome sequence, the functional diversity encoded therein, and the presence of some pathways missing from other model organisms makes T. thermophila an ideal model for functional genomic studies to address biological, biomedical, and biotechnological questions of fundamental importance.

Dataset Information

A micronucleus-specific sequence exists in the 5'-upstream region of calmodulin gene in Tetrahymena thermophila.

Publications

A micronucleus-specific sequence exists in the 5'-upstream region of calmodulin gene in Tetrahymena thermophila.

Similar Datasets

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