Structural Analysis of TRAS1, a Novel Family of Telomeric Repeat-Associated Retrotransposons in the Silkworm, <i>Bombyx mori</i>

Okazaki, Satoshi; Ishikawa, Hajime; Fujiwara, Haruhiko

doi:10.1128/mcb.15.8.4545

Cited by 106 publications

(102 citation statements)

References 54 publications

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“…In further study, it will be clarified whether some components of Bombyx telomerase are blocked functionally and what mechanisms underlie the (TTAGG) n addition under such a low telomerase activity. In Bombyx telomeres, hundreds of copies of several families of nonLTR retrotransposons (LINE-like elements) are accumulated within the telomeric repeats [33,34]. These telomeric repeat associated retrotransposons, named TRAS and SART, are actively transcribed and possibly work on telomere elongation [35].…”

Section: Discussionmentioning

confidence: 99%

Detection and distribution patterns of telomerase activity in insects

Sasaki¹,

Fujiwara²

2000

Eur J Biochem

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Telomeres of most insects consist of pentanucleotide (TTAGG) n repeats, although the repeats are absent in Diptera and some other insect species, where the telomere regions are perhaps maintained without telomerase. To understand various and unusual telomere formation in insects, we have studied the characteristic features of a putative insect telomerase that has not been previously described. Using a modified telomeric repeat amplification protocol (TRAP), we first detected the telomerase activity in crickets, cockroaches and two Lepidopteran insects. The telomerase from crickets and cockroaches required dATP, dGTP and dTTP but not dCTP as a substrate and sequence analyses of the products of TRAP revealed that the (TTAGG) n repeats are synthesized by telomerase. The cockroach telomerase was detected both in somatic (fat body, muscle and neural tissues) and germ line (testis) cells, suggesting that expression of this enzyme is not regulated in a tissue-specific manner at an adult stage. While we detected high levels of telomerase activity in crickets and cockroaches, we could not detect activity in all tissues and cell cultures of the silkworm, Bombyx mori and in two Drosophila and one Sarcophaga cell lines. This supports the theory that Dipteran insects maintain their telomeres without telomerase.

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Section: Discussionmentioning

confidence: 99%

Detection and distribution patterns of telomerase activity in insects

Sasaki¹,

Fujiwara²

2000

Eur J Biochem

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“…In two regions, which are shown by gray lines under the sequences, LINEs have shorter amino acid tracts compared with that of APE1. Secondary structural information (␣1-3, ␤1-14, 3 10 A, and 3 10 B) obtained by crystal analyses is shown above the amino acid sequences. The amino acids altered in mutagenesis studies (Fig.…”

Section: Tras1-en Efficiently Digests Both (Ttagg) N and (Ttag-gg) N mentioning

confidence: 99%

“…However, several endonuclease-encoding LINE have very restricted integration targets within the genome (9). TRAS1 and R1Bm, found in Bombyx mori, are the typical sequence-specific elements, which insert between T and A of the (TTAGG) n telomeric repeat and a specific site in 28 S rDNA of B. mori, respectively (10,11). Recent studies have shown that the endonuclease domain in the ORF2 of TRAS1 (12) and R1Bm (13) determines its own target sequence recognition and DNA cleavage activity.…”

mentioning

confidence: 99%

Crystal Structure of the Endonuclease Domain Encoded by the Telomere-specific Long Interspersed Nuclear Element, TRAS1

Maita

Anzai

Aoyagi

et al. 2004

Journal of Biological Chemistry

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The telomere-specific long interspersed nuclear element, TRAS1, encodes an endonuclease domain, TRAS1-EN, which specifically cleaves the telomeric repeat targets (TTAGG) n of insects and (TTAGGG) n of vertebrates. To elucidate the sequence-specific recognition properties of TRAS1-EN, we determined the crystal structure at 2.4-Å resolution. TRAS1-EN has a four-layered ␣/␤ sandwich structure; its topology is similar to apurinic/ apyrimidinic endonucleases, but the ␤-hairpin (␤ 10 -␤ 11 ) at the edge of the DNA-binding surface makes an extra loop that distinguishes TRAS1-EN from cellular apurinic/apyrimidinic endonucleases. A protein-DNA complex model suggests that the ␤ 10 -␤ 11 hairpin fits into the minor groove, enabling interaction with the telomeric repeats. Mutational studies of TRAS1-EN also indicated that the Asp-130 and ␤ 10 -␤ 11 hairpin structure are involved in specific recognition of telomeric repeats.Non-long terminal repeat retrotransposons, also known as long interspersed nuclear elements (LINEs), 1 are transposable elements that encode a reverse transcriptase and insert into genomic locations via RNA intermediates. The recent progress of the human genome project has revealed that one LINE, L1, integrates throughout chromosomes and occupies more than 20% of the genome (1). The integration of L1 may play a role in genetic diseases and cancers (2) and in gene evolution and genome reconstruction (3-5).The LINEs have been classified into two types according to the number of open reading frames (ORFs) (6). The first type of element has a single ORF and encodes an endonuclease domain near its C terminus; this type of endonuclease (also known as restriction enzyme-like endonuclease) is similar in some residual motifs to various prokaryotic restriction enzymes (7). The second type of element has two ORFs; ORF1 encodes a retroviral Gag-like protein whose function is still unclear, and ORF2 encodes a protein with an endonuclease domain at its N terminus and a reverse transcriptase domain in the center of the ORF. This class of endonuclease domain is made up of about 250 amino acid residues and shares sequence homology with apurinic/apyrimidinic endonucleases (APE), such as human APE1 and Escherichia coli exonuclease III.Most of the APE-like endonuclease-encoding retrotransposons do not insert in a sequence-specific manner into the host genome, like the human L1 elements that cleave AT-rich sequences with a low sequence specificity (8). However, several endonuclease-encoding LINE have very restricted integration targets within the genome (9). TRAS1 and R1Bm, found in Bombyx mori, are the typical sequence-specific elements, which insert between T and A of the (TTAGG) n telomeric repeat and a specific site in 28 S rDNA of B. mori, respectively (10, 11). Recent studies have shown that the endonuclease domain in the ORF2 of TRAS1 (12) and R1Bm (13) determines its own target sequence recognition and DNA cleavage activity.The amino acid identity between human APE1 and the endonuclease domain of TRAS1 (TRAS1-EN) is n...

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“…The telomeres of the silkworm consist of the insect telomeric repeats but harbor many types of non-LTR retrotransposons, designated TRAS and SART families (Fujiwara et al, 2005;Kubo et al, 2001;Okazaki et al, 1995). TRAS and SART are abundantly transcribed and actively transpose into TTAGG telomeric repeats in a highly sequence-specific manner.…”

Section: The Silkwormmentioning

confidence: 99%