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2001
Wilhelm M., Uzun O., Mules E. H., Gabriel A., Wilhelm F. X.
Polypurine tract formation by Ty1 RNase H Journal Article
In: J Biol Chem, vol. 276, no. 50, pp. 47695-701, 2001, (0021-9258 Journal Article).
Abstract | BibTeX | Tags: *Purines, *Retroelements, Base, Binding, Calf, Data, DNA, DNA/metabolism, Factors, Gov't, H, Hydrolysis, Molecular, Mutation, Non-U.S., P.H.S., Polymerase/*chemistry/*metabolism, Primers/pharmacology, Protein, Proteins/metabolism, Recombinant, Ribonuclease, RNA-Directed, RNA/metabolism, Sequence, Sites, Support, Thymus/*chemistry/*genetics/metabolism, time, U.S.
@article{,
title = {Polypurine tract formation by Ty1 RNase H},
author = { M. Wilhelm and O. Uzun and E. H. Mules and A. Gabriel and F. X. Wilhelm},
year = {2001},
date = {2001-01-01},
journal = {J Biol Chem},
volume = {276},
number = {50},
pages = {47695-701},
abstract = {To better understand the mechanism by which Ty1 RNase H creates the polypurine tract (PPT) primer, we have demonstrated the polymerase-dependent hydrolytic activity of Ty1 reverse transcriptase (RT) during minus-strand synthesis. Using RNase H and polymerase mutants of the recombinant Ty1 RT protein, we show that the two domains of Ty1 RT can act independently of one another. Our results indicate that RNA/DNA substrates containing a short RNA PPT, which serve as primers for plus-strand DNA synthesis, are relatively resistant to RNase H cleavage. RNA substrates with a correct 5' end but with 3' end extending beyond the plus-strand initiation site were cleaved specifically to generate the correct 3' end of the PPT. Using long RNA/DNA duplexes containing the PPT, we show that Ty1 RT is able to make specific internal cleavages that could generate the plus-strand primer with correct 5' and 3' ends. Long RNA/DNA duplexes with mutations in the PPT or in a U-rich region upstream of the PPT, which abolish plus-strand initiation in vivo, were not cleaved specifically at the 5' end of the PPT. Our work demonstrates that the in vitro enzyme can recapitulate key processes that control proper replication in vivo.},
note = {0021-9258
Journal Article},
keywords = {*Purines, *Retroelements, Base, Binding, Calf, Data, DNA, DNA/metabolism, Factors, Gov't, H, Hydrolysis, Molecular, Mutation, Non-U.S., P.H.S., Polymerase/*chemistry/*metabolism, Primers/pharmacology, Protein, Proteins/metabolism, Recombinant, Ribonuclease, RNA-Directed, RNA/metabolism, Sequence, Sites, Support, Thymus/*chemistry/*genetics/metabolism, time, U.S.},
pubstate = {published},
tppubtype = {article}
}
To better understand the mechanism by which Ty1 RNase H creates the polypurine tract (PPT) primer, we have demonstrated the polymerase-dependent hydrolytic activity of Ty1 reverse transcriptase (RT) during minus-strand synthesis. Using RNase H and polymerase mutants of the recombinant Ty1 RT protein, we show that the two domains of Ty1 RT can act independently of one another. Our results indicate that RNA/DNA substrates containing a short RNA PPT, which serve as primers for plus-strand DNA synthesis, are relatively resistant to RNase H cleavage. RNA substrates with a correct 5' end but with 3' end extending beyond the plus-strand initiation site were cleaved specifically to generate the correct 3' end of the PPT. Using long RNA/DNA duplexes containing the PPT, we show that Ty1 RT is able to make specific internal cleavages that could generate the plus-strand primer with correct 5' and 3' ends. Long RNA/DNA duplexes with mutations in the PPT or in a U-rich region upstream of the PPT, which abolish plus-strand initiation in vivo, were not cleaved specifically at the 5' end of the PPT. Our work demonstrates that the in vitro enzyme can recapitulate key processes that control proper replication in vivo.
Wilhelm M., Wilhelm F. X.
Reverse transcription of retroviruses and LTR retrotransposons Journal Article
In: Cell Mol Life Sci, vol. 58, no. 9, pp. 1246-62, 2001, (1420-682x Journal Article Review Review, Academic).
Abstract | BibTeX | Tags: *Retroelements, *Terminal, Acid, Alignment, Amino, Animals, Base, Conformation, Data, DNA, Homology, Human, Molecular, Nucleic, Polymerase/*chemistry/*metabolism, Repeat, Retroviridae/*enzymology/*genetics, RNA-Directed, Sequence, Sequences
@article{,
title = {Reverse transcription of retroviruses and LTR retrotransposons},
author = { M. Wilhelm and F. X. Wilhelm},
year = {2001},
date = {2001-01-01},
journal = {Cell Mol Life Sci},
volume = {58},
number = {9},
pages = {1246-62},
abstract = {Retroelements are mobile genetic entities that replicate via reverse transcription of a template RNA. A key component to the life cycle of these elements is the enzyme reverse transcriptase (RT), which copies the single-stranded genomic RNA of the element into a linear double-stranded DNA that is ultimately integrated into the host genome by the element-encoded integrase. RT is a multifunctionnal enzyme which possesses RNA-dependent and DNA-dependent DNA polymerase activities as well as RNase H activity that specifically degrades the RNA strand of RNA-DNA duplexes. At some stages of the replication a strand-displacement activity of RT is also necessary. All activities are essential for the conversion of single-stranded genomic RNA into the double-stranded preintegrative DNA. This review focuses on the role of RT in the different steps of the replication process of retroelements. The features of retrotransposon replication which differ from the retroviral ones will be emphasized. In a second part of the review, the biochemical and enzymatic properties of two newly characterized retrotransposon RTs will be described. The role of the integrase domain in reverse transcriptase activity of some retroviral and retrotransposon RTs will be discussed.},
note = {1420-682x
Journal Article
Review
Review, Academic},
keywords = {*Retroelements, *Terminal, Acid, Alignment, Amino, Animals, Base, Conformation, Data, DNA, Homology, Human, Molecular, Nucleic, Polymerase/*chemistry/*metabolism, Repeat, Retroviridae/*enzymology/*genetics, RNA-Directed, Sequence, Sequences},
pubstate = {published},
tppubtype = {article}
}
Retroelements are mobile genetic entities that replicate via reverse transcription of a template RNA. A key component to the life cycle of these elements is the enzyme reverse transcriptase (RT), which copies the single-stranded genomic RNA of the element into a linear double-stranded DNA that is ultimately integrated into the host genome by the element-encoded integrase. RT is a multifunctionnal enzyme which possesses RNA-dependent and DNA-dependent DNA polymerase activities as well as RNase H activity that specifically degrades the RNA strand of RNA-DNA duplexes. At some stages of the replication a strand-displacement activity of RT is also necessary. All activities are essential for the conversion of single-stranded genomic RNA into the double-stranded preintegrative DNA. This review focuses on the role of RT in the different steps of the replication process of retroelements. The features of retrotransposon replication which differ from the retroviral ones will be emphasized. In a second part of the review, the biochemical and enzymatic properties of two newly characterized retrotransposon RTs will be described. The role of the integrase domain in reverse transcriptase activity of some retroviral and retrotransposon RTs will be discussed.
1999
Wilhelm M., Boutabout M., Heyman T., Wilhelm F. X.
Reverse transcription of the yeast Ty1 retrotransposon: the mode of first strand transfer is either intermolecular or intramolecular Journal Article
In: J Mol Biol, vol. 288, no. 4, pp. 505-10, 1999, (0022-2836 Journal Article).
Abstract | BibTeX | Tags: *Retroelements, *Transcription, Acid, Base, cerevisiae/*genetics, DNA, Genetic, Gov't, Non-U.S., Nucleic, Repetitive, Saccharomyces, Sequence, Sequences, Single-Stranded/genetics, Support
@article{,
title = {Reverse transcription of the yeast Ty1 retrotransposon: the mode of first strand transfer is either intermolecular or intramolecular},
author = { M. Wilhelm and M. Boutabout and T. Heyman and F. X. Wilhelm},
year = {1999},
date = {1999-01-01},
journal = {J Mol Biol},
volume = {288},
number = {4},
pages = {505-10},
abstract = {Replication of the yeast Ty1 retrotransposon occurs by a mechanism similar to that of retroviruses. According to the current model of retroviral reverse transcription, two strand transfers (the so-called minus-strand and plus-strand strong-stop DNA transfers) are required to produce full-length preintegrative DNA. Because two genomic RNA molecules are packaged inside the viral particles, the strand transfers can be either intra- or intermolecular. To study the mode of transfer of minus-strand strong-stop DNA during reverse transcription of the yeast Ty1 retrotransposon, we have analyzed the cDNA products that accumulate in the cytoplasmic virus-like particles of yeast cells harboring two marked Ty1 elements. Our results indicate that Ty1 minus-strand transfer occurs in a random manner with approximately similar frequencies of intra- and intermolecular transfer. It has been observed recently that intra- and intermolecular minus-strand transfer occur at similar frequencies during replication of a complex retrovirus such as HIV-1. These results together with the observation that genetic recombination occurs with a high frequency during minus-strand synthesis suggest that both packaged RNA molecules are needed for the synthesis of one minus-strand DNA.},
note = {0022-2836
Journal Article},
keywords = {*Retroelements, *Transcription, Acid, Base, cerevisiae/*genetics, DNA, Genetic, Gov't, Non-U.S., Nucleic, Repetitive, Saccharomyces, Sequence, Sequences, Single-Stranded/genetics, Support},
pubstate = {published},
tppubtype = {article}
}
Replication of the yeast Ty1 retrotransposon occurs by a mechanism similar to that of retroviruses. According to the current model of retroviral reverse transcription, two strand transfers (the so-called minus-strand and plus-strand strong-stop DNA transfers) are required to produce full-length preintegrative DNA. Because two genomic RNA molecules are packaged inside the viral particles, the strand transfers can be either intra- or intermolecular. To study the mode of transfer of minus-strand strong-stop DNA during reverse transcription of the yeast Ty1 retrotransposon, we have analyzed the cDNA products that accumulate in the cytoplasmic virus-like particles of yeast cells harboring two marked Ty1 elements. Our results indicate that Ty1 minus-strand transfer occurs in a random manner with approximately similar frequencies of intra- and intermolecular transfer. It has been observed recently that intra- and intermolecular minus-strand transfer occur at similar frequencies during replication of a complex retrovirus such as HIV-1. These results together with the observation that genetic recombination occurs with a high frequency during minus-strand synthesis suggest that both packaged RNA molecules are needed for the synthesis of one minus-strand DNA.
Wilhelm M., Heyman T., Boutabout M., Wilhelm F. X.
A sequence immediately upstream of the plus-strand primer is essential for plus-strand DNA synthesis of the Saccharomyces cerevisiae Ty1 retrotransposon Journal Article
In: Nucleic Acids Res, vol. 27, no. 23, pp. 4547-52, 1999, (0305-1048 Journal Article).
Abstract | BibTeX | Tags: *DNA, *Retroelements, Base, cerevisiae/*genetics, DNA, Elements, Fungal/*biosynthesis, Gov't, Mutation, Non-U.S., Primers, response, Saccharomyces, Sequence, Support
@article{,
title = {A sequence immediately upstream of the plus-strand primer is essential for plus-strand DNA synthesis of the Saccharomyces cerevisiae Ty1 retrotransposon},
author = { M. Wilhelm and T. Heyman and M. Boutabout and F. X. Wilhelm},
year = {1999},
date = {1999-01-01},
journal = {Nucleic Acids Res},
volume = {27},
number = {23},
pages = {4547-52},
abstract = {Priming of plus-strand DNA is a critical step in reverse transcription of retroviruses and retrotransposons. All retroelements use an RNase H-resistant oligoribonucleotide spanning a purine-rich sequence (the polypurine tract or PPT) to prime plus-strand DNA synthesis. Plus-strand DNA synthesis of the yeast Saccharomyces cerevisiae Ty1-H3 retrotransposon is initiated at two sites, PPT1 and PPT2, located at the upstream boundary of the 3'-long terminal repeat and near the middle of the pol gene in the integrase coding region. The two plus-strand primers have the same purine-rich sequence GGGTGGTA. This sequence is not sufficient by itself to generate a plus-strand origin since two identical sequences located upstream of PPT2 in the integrase coding region are not used efficiently as primers for plus-strand DNA synthesis. Thus, other factors must be involved in the formation of a specific plus-strand DNA primer. We show here that mutations upstream of the PPT in a highly conserved T-rich region severely alters plus-strand DNA priming of Ty1. Our results demonstrate the importance of sequences or structural elements upstream of the PPT for initiation of plus-strand DNA synthesis.},
note = {0305-1048
Journal Article},
keywords = {*DNA, *Retroelements, Base, cerevisiae/*genetics, DNA, Elements, Fungal/*biosynthesis, Gov't, Mutation, Non-U.S., Primers, response, Saccharomyces, Sequence, Support},
pubstate = {published},
tppubtype = {article}
}
Priming of plus-strand DNA is a critical step in reverse transcription of retroviruses and retrotransposons. All retroelements use an RNase H-resistant oligoribonucleotide spanning a purine-rich sequence (the polypurine tract or PPT) to prime plus-strand DNA synthesis. Plus-strand DNA synthesis of the yeast Saccharomyces cerevisiae Ty1-H3 retrotransposon is initiated at two sites, PPT1 and PPT2, located at the upstream boundary of the 3'-long terminal repeat and near the middle of the pol gene in the integrase coding region. The two plus-strand primers have the same purine-rich sequence GGGTGGTA. This sequence is not sufficient by itself to generate a plus-strand origin since two identical sequences located upstream of PPT2 in the integrase coding region are not used efficiently as primers for plus-strand DNA synthesis. Thus, other factors must be involved in the formation of a specific plus-strand DNA primer. We show here that mutations upstream of the PPT in a highly conserved T-rich region severely alters plus-strand DNA priming of Ty1. Our results demonstrate the importance of sequences or structural elements upstream of the PPT for initiation of plus-strand DNA synthesis.
1998
Friant S., Heyman T., Bystrom A. S., Wilhelm M., Wilhelm F. X.
Interactions between Ty1 retrotransposon RNA and the T and D regions of the tRNA(iMet) primer are required for initiation of reverse transcription in vivo Journal Article
In: Mol Cell Biol, vol. 18, no. 2, pp. 799-806, 1998, (0270-7306 Journal Article).
Abstract | BibTeX | Tags: *Retroelements, *Transcription, Acid, Base, Binding, cerevisiae, Conformation, Data, DNA, Fungal/*metabolism, Fungal/biosynthesis, Genetic, Gov't, Met/*metabolism, Molecular, Mutagenesis, Non-U.S., Nucleic, Primers, Replication, RNA, Saccharomyces, Sequence, Sites, Support, Transfer
@article{,
title = {Interactions between Ty1 retrotransposon RNA and the T and D regions of the tRNA(iMet) primer are required for initiation of reverse transcription in vivo},
author = { S. Friant and T. Heyman and A. S. Bystrom and M. Wilhelm and F. X. Wilhelm},
year = {1998},
date = {1998-01-01},
journal = {Mol Cell Biol},
volume = {18},
number = {2},
pages = {799-806},
abstract = {Reverse transcription of the Saccharomyces cerevisiae Ty1 retrotransposon is primed by tRNA(iMet) base paired to the primer binding site (PBS) near the 5' end of Ty1 genomic RNA. The 10-nucleotide PBS is complementary to the last 10 nucleotides of the acceptor stem of tRNA(iMet). A structural probing study of the interactions between the Ty1 RNA template and the tRNA(iMet) primer showed that besides interactions between the PBS and the 3' end of tRNA(iMet), three short regions of Ty1 RNA, named boxes 0, 1, and 2.1, interact with the T and D stems and loops of tRNA(iMet). To determine if these sequences are important for the reverse transcription pathway of the Ty1 retrotransposon, mutant Ty1 elements and tRNA(iMet) were tested for the ability to support transposition. We show that the Ty1 boxes and the complementary sequences in the T and D stems and loops of tRNA(iMet) contain bases that are critical for Ty1 retrotransposition. Disruption of 1 or 2 bp between tRNA(iMet) and box 0, 1, or 2.1 dramatically decreases the level of transposition. Compensatory mutations which restore base pairing between the primer and the template restore transposition. Analysis of the reverse transcription intermediates generated inside Ty1 virus-like particles indicates that initiation of minus-strand strong-stop DNA synthesis is affected by mutations disrupting complementarity between Ty1 RNA and primer tRNA(iMet).},
note = {0270-7306
Journal Article},
keywords = {*Retroelements, *Transcription, Acid, Base, Binding, cerevisiae, Conformation, Data, DNA, Fungal/*metabolism, Fungal/biosynthesis, Genetic, Gov't, Met/*metabolism, Molecular, Mutagenesis, Non-U.S., Nucleic, Primers, Replication, RNA, Saccharomyces, Sequence, Sites, Support, Transfer},
pubstate = {published},
tppubtype = {article}
}
Reverse transcription of the Saccharomyces cerevisiae Ty1 retrotransposon is primed by tRNA(iMet) base paired to the primer binding site (PBS) near the 5' end of Ty1 genomic RNA. The 10-nucleotide PBS is complementary to the last 10 nucleotides of the acceptor stem of tRNA(iMet). A structural probing study of the interactions between the Ty1 RNA template and the tRNA(iMet) primer showed that besides interactions between the PBS and the 3' end of tRNA(iMet), three short regions of Ty1 RNA, named boxes 0, 1, and 2.1, interact with the T and D stems and loops of tRNA(iMet). To determine if these sequences are important for the reverse transcription pathway of the Ty1 retrotransposon, mutant Ty1 elements and tRNA(iMet) were tested for the ability to support transposition. We show that the Ty1 boxes and the complementary sequences in the T and D stems and loops of tRNA(iMet) contain bases that are critical for Ty1 retrotransposition. Disruption of 1 or 2 bp between tRNA(iMet) and box 0, 1, or 2.1 dramatically decreases the level of transposition. Compensatory mutations which restore base pairing between the primer and the template restore transposition. Analysis of the reverse transcription intermediates generated inside Ty1 virus-like particles indicates that initiation of minus-strand strong-stop DNA synthesis is affected by mutations disrupting complementarity between Ty1 RNA and primer tRNA(iMet).
Gabus C., Ficheux D., Rau M., Keith G., Sandmeyer S., Darlix J. L.
The yeast Ty3 retrotransposon contains a 5'-3' bipartite primer-binding site and encodes nucleocapsid protein NCp9 functionally homologous to HIV-1 NCp7 Journal Article
In: EMBO J, vol. 17, no. 16, pp. 4873-80, 1998, (0261-4189 Journal Article).
Abstract | BibTeX | Tags: *Capsid, *Retroelements, Acid, Base, Binding, Capsid/*genetics, cerevisiae/*genetics, dimerization, gag/*genetics, Gene, Gov't, Homology, Met/genetics/*metabolism, Non-U.S., Nucleic, P.H.S., Products, Proteins, RNA, Saccharomyces, Sequence, Sites, Support, Transfer, U.S.
@article{,
title = {The yeast Ty3 retrotransposon contains a 5'-3' bipartite primer-binding site and encodes nucleocapsid protein NCp9 functionally homologous to HIV-1 NCp7},
author = { C. Gabus and D. Ficheux and M. Rau and G. Keith and S. Sandmeyer and J. L. Darlix},
year = {1998},
date = {1998-01-01},
journal = {EMBO J},
volume = {17},
number = {16},
pages = {4873-80},
abstract = {Retroviruses, including HIV-1 and the distantly related yeast retroelement Ty3, all encode a nucleoprotein required for virion structure and replication. During an in vitro comparison of HIV-1 and Ty3 nucleoprotein function in RNA dimerization and cDNA synthesis, we discovered a bipartite primer-binding site (PBS) for Ty3 composed of sequences located at opposite ends of the genome. Ty3 cDNA synthesis requires the 3' PBS for primer tRNAiMet annealing to the genomic RNA, and the 5' PBS, in cis or in trans, as the reverse transcription start site. Ty3 RNA alone is unable to dimerize, but formation of dimeric tRNAiMet bound to the PBS was found to direct dimerization of Ty3 RNA-tRNAiMet. Interestingly, HIV-1 nucleocapsid protein NCp7 and Ty3 NCp9 were interchangeable using HIV-1 and Ty3 RNA template-primer systems. Our findings impact on the understanding of non-canonical reverse transcription as well as on the use of Ty3 systems to screen for anti-NCp7 drugs.},
note = {0261-4189
Journal Article},
keywords = {*Capsid, *Retroelements, Acid, Base, Binding, Capsid/*genetics, cerevisiae/*genetics, dimerization, gag/*genetics, Gene, Gov't, Homology, Met/genetics/*metabolism, Non-U.S., Nucleic, P.H.S., Products, Proteins, RNA, Saccharomyces, Sequence, Sites, Support, Transfer, U.S.},
pubstate = {published},
tppubtype = {article}
}
Retroviruses, including HIV-1 and the distantly related yeast retroelement Ty3, all encode a nucleoprotein required for virion structure and replication. During an in vitro comparison of HIV-1 and Ty3 nucleoprotein function in RNA dimerization and cDNA synthesis, we discovered a bipartite primer-binding site (PBS) for Ty3 composed of sequences located at opposite ends of the genome. Ty3 cDNA synthesis requires the 3' PBS for primer tRNAiMet annealing to the genomic RNA, and the 5' PBS, in cis or in trans, as the reverse transcription start site. Ty3 RNA alone is unable to dimerize, but formation of dimeric tRNAiMet bound to the PBS was found to direct dimerization of Ty3 RNA-tRNAiMet. Interestingly, HIV-1 nucleocapsid protein NCp7 and Ty3 NCp9 were interchangeable using HIV-1 and Ty3 RNA template-primer systems. Our findings impact on the understanding of non-canonical reverse transcription as well as on the use of Ty3 systems to screen for anti-NCp7 drugs.
1995
Heyman T., Agoutin B., Friant S., Wilhelm F. X., Wilhelm M. L.
Plus-strand DNA synthesis of the yeast retrotransposon Ty1 is initiated at two sites, PPT1 next to the 3' LTR and PPT2 within the pol gene. PPT1 is sufficient for Ty1 transposition Journal Article
In: J Mol Biol, vol. 253, no. 2, pp. 291-303, 1995, (0022-2836 Journal Article).
Abstract | BibTeX | Tags: *DNA, *Genes, *Repetitive, *Retroelements, Acid, Base, C/analysis, cerevisiae/genetics/*virology, Chain, Cloning, Data, DNA, Fungal, Fungal/biosynthesis, Genes, Genetic, Genome, Gov't, Mapping, Molecular, Non-U.S., Nucleic, pol, Poly, Polymerase, Primers, Reaction, Replication, Restriction, Saccharomyces, Sequence, Sequences, Support, Transcription, Viral, Viral/*biosynthesis
@article{,
title = {Plus-strand DNA synthesis of the yeast retrotransposon Ty1 is initiated at two sites, PPT1 next to the 3' LTR and PPT2 within the pol gene. PPT1 is sufficient for Ty1 transposition},
author = { T. Heyman and B. Agoutin and S. Friant and F. X. Wilhelm and M. L. Wilhelm},
year = {1995},
date = {1995-01-01},
journal = {J Mol Biol},
volume = {253},
number = {2},
pages = {291-303},
abstract = {Long terminal repeat elements and retroviruses require primers for initiation of minus and plus-strand DNA synthesis by reverse transcriptase. Here we demonstrate genetically that plus-strand DNA synthesis of the yeast Ty1 element is initiated at two sites located at the 5' boundary of the 3' long terminal repeat (PPT1) and near the middle of the pol gene in the integrase coding sequence (PPT2). A consequence of the presence of two PPTs is that Ty1 plus-strand DNA exists as segments at some time during replication. Three fragments have been identified: the plus-strand strong-stop DNA initiated at PPT1, a downstream fragment initiated at PPT2 and an upstream fragment spanning the 5'-terminal part of Ty1 and a portion of the TyB gene. Characterization of the 3' ends of the plus-strand DNA fragments reveals (1) that the upstream fragment is elongated beyond PPT2 creating a plus-strand overlap and (2) that the majority of plus-strand strong-stop DNA fragments bear a copy of the minus-strand primer binding site in agreement with the accepted model of retroviral genomic RNA reverse transcription. The two polypurine tracts, PPT1 and PPT2, have an identical sequence GGGTGGTA. Mutations replacing purines by pyrimidines in this sequence significantly diminish or abolish initiation of plus-strand synthesis. Ty1 elements bearing a mutated PPT2 sequence are not defective for transposition whereas mutations in PPT1 abolish transposition.},
note = {0022-2836
Journal Article},
keywords = {*DNA, *Genes, *Repetitive, *Retroelements, Acid, Base, C/analysis, cerevisiae/genetics/*virology, Chain, Cloning, Data, DNA, Fungal, Fungal/biosynthesis, Genes, Genetic, Genome, Gov't, Mapping, Molecular, Non-U.S., Nucleic, pol, Poly, Polymerase, Primers, Reaction, Replication, Restriction, Saccharomyces, Sequence, Sequences, Support, Transcription, Viral, Viral/*biosynthesis},
pubstate = {published},
tppubtype = {article}
}
Long terminal repeat elements and retroviruses require primers for initiation of minus and plus-strand DNA synthesis by reverse transcriptase. Here we demonstrate genetically that plus-strand DNA synthesis of the yeast Ty1 element is initiated at two sites located at the 5' boundary of the 3' long terminal repeat (PPT1) and near the middle of the pol gene in the integrase coding sequence (PPT2). A consequence of the presence of two PPTs is that Ty1 plus-strand DNA exists as segments at some time during replication. Three fragments have been identified: the plus-strand strong-stop DNA initiated at PPT1, a downstream fragment initiated at PPT2 and an upstream fragment spanning the 5'-terminal part of Ty1 and a portion of the TyB gene. Characterization of the 3' ends of the plus-strand DNA fragments reveals (1) that the upstream fragment is elongated beyond PPT2 creating a plus-strand overlap and (2) that the majority of plus-strand strong-stop DNA fragments bear a copy of the minus-strand primer binding site in agreement with the accepted model of retroviral genomic RNA reverse transcription. The two polypurine tracts, PPT1 and PPT2, have an identical sequence GGGTGGTA. Mutations replacing purines by pyrimidines in this sequence significantly diminish or abolish initiation of plus-strand synthesis. Ty1 elements bearing a mutated PPT2 sequence are not defective for transposition whereas mutations in PPT1 abolish transposition.
