Dataset Information

A proposed superfamily of transposase genes: transposon-like elements in ciliated protozoa and a common "D35E" motif.

ABSTRACT: The transposon-like elements TBE1, Tec1, and Tec2 of hypotrichous ciliated protozoa appear to encode a protein that belongs to the IS630-Tc1 family of transposases. The Anabaena IS895 transposase also is placed in this family. We note that most family members transpose into the dinucleotide target, TA, and that members with eukaryotic hosts have a tendency for somatic excision that is carried to an extreme by the ciliate elements. Alignments including the additional members, and also mariner elements, show that transposases of this family share strongly conserved residues in a large C-terminal portion, including a fully conserved dipeptide, Asp-Glu (DE), and a block consisting of a fully conserved Asp and highly conserved Glu, separated by 34 or 35 residues (D35E). This D35E motif likely is homologous to the previously characterized D35E motif of the family of retroviral-retrotransposon integrases and IS3-like transposases. Because it is known that the IS3-retroposon D35E region is a critical portion of a domain capable of various in vitro transposition-related reactions, the results suggest that the two families share homologous catalytic transposase domains and that members of both families may share a common transposition mechanism.

SUBMITTER: Doak TG

PROVIDER: S-EPMC521429 | biostudies-other | 1994 Feb

REPOSITORIES: biostudies-other

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A proposed superfamily of transposase genes: transposon-like elements in ciliated protozoa and a common "D35E" motif.

Doak T G TG Doerder F P FP Jahn C L CL Herrick G G

Proceedings of the National Academy of Sciences of the United States of America 19940201 3

The transposon-like elements TBE1, Tec1, and Tec2 of hypotrichous ciliated protozoa appear to encode a protein that belongs to the IS630-Tc1 family of transposases. The Anabaena IS895 transposase also is placed in this family. We note that most family members transpose into the dinucleotide target, TA, and that members with eukaryotic hosts have a tendency for somatic excision that is carried to an extreme by the ciliate elements. Alignments including the additional members, and also mariner ele ...[more]

PMID: 8302872

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Project description:BackgroundTransposable elements (TEs) are the most abundant genomic components in eukaryotes and affect the genome by their replications and movements to generate genetic plasticity. Sweet potato performs asexual reproduction generally and the TEs may be an important genetic factor for genome reorganization. Complete identification of TEs is essential for the study of genome evolution. However, the TEs of sweet potato are still poorly understood because of its complex hexaploid genome and difficulty in genome sequencing. The recent availability of the sweet potato transcriptome databases provides an opportunity for discovering and characterizing the expressed TEs.Methodology/principal findingsWe first established the integrated-transcriptome database by de novo assembling four published sweet potato transcriptome databases from three cultivars in China. Using sequence-similarity search and analysis, a total of 1,405 TEs including 883 retrotransposons and 522 DNA transposons were predicted and categorized. Depending on mapping sets of RNA-Seq raw short reads to the predicted TEs, we compared the quantities, classifications and expression activities of TEs inter- and intra-cultivars. Moreover, the differential expressions of TEs in seven tissues of Xushu 18 cultivar were analyzed by using Illumina digital gene expression (DGE) tag profiling. It was found that 417 TEs were expressed in one or more tissues and 107 in all seven tissues. Furthermore, the copy number of 11 transposase genes was determined to be 1-3 copies in the genome of sweet potato by Real-time PCR-based absolute quantification.Conclusions/significanceOur result provides a new method for TE searching on species with transcriptome sequences while lacking genome information. The searching, identification and expression analysis of TEs will provide useful TE information in sweet potato, which are valuable for the further studies of TE-mediated gene mutation and optimization in asexual reproduction. It contributes to elucidating the roles of TEs in genome evolution.

Project description:Protistan bacterivory, a microbial process involving ingestion and digestion, is ecologically important in the microbial loop in aquatic and terrestrial ecosystems. While bacterial resistance to protistan ingestion has been relatively well understood, little is known about protistan digestion in which some ingested bacteria could not be digested in cells of major protistan grazers in the natural environment. Here we report the phylogenetic identities of digestion-resistant bacteria (DRB) that could survive starvation and form relatively stable associations with 11 marine and one freshwater ciliate species. Using clone library and sequencing of 16S rRNA genes, we found that the protistan predators could host a high diversity of DRB, most of which represented novel bacterial taxa that have not been cultivated. The localization inside host cells, quantity, and viability of these bacteria were checked using fluorescence in situ hybridization. The DRB were affiliated with Actinobacteria, Bacteroidetes, Firmicutes, Parcubacteria (OD1), Planctomycetes, and Proteobacteria, with Gammaproteobacteria and Alphaproteobacteria being the most frequently occurring classes. The dominance of Gamma- and Alphaproteobacteria corresponds well to a previous study of Global Ocean Sampling metagenomic data showing the widespread types of bacterial type VI and IV secretion systems (T6SS and T4SS) in these two taxa, suggesting a putatively significant role of secretion systems in promoting marine protist-bacteria associations. In the DRB assemblages, opportunistic bacteria such as Alteromonadaceae, Pseudoalteromonadaceae, and Vibrionaceae often presented with high proportions, indicating these bacteria could evade protistan grazing thus persist and accumulate in the community, which, however, contrasts with their well-known rarity in nature. This begs the question whether viral lysis is significant in killing these indigestible bacteria in microbial communities. Taken together, our study on the identity of DRB sheds new light on microbial interactions and generates further hypotheses including the potential importance of bacterial protein secretion systems in structuring bacterial community composition and functioning of "microbial black box" in aquatic environments.

Dataset Information

A proposed superfamily of transposase genes: transposon-like elements in ciliated protozoa and a common "D35E" motif.

Publications

A proposed superfamily of transposase genes: transposon-like elements in ciliated protozoa and a common "D35E" motif.

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