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Human protein binding to DNA sequences surrounding the human T-cell lymphotropic virus type-I long terminal repeat
Abstract:
The long terminal repeats (LTRs) of RNA tumor viruses, including human T-cell lymphotropic virus type I (HTLV-I), contain the control elements for expression of viral genes. Sequence-specific LTR-DNA-binding proteins could regulate viral functions. To search for such proteins we have used an in vitro non-denaturing polyacrylamide gel assay, with restriction fragments of the HTLV-I LTR and nuclear protein extracts from several HTLV-I-infected cell lines and an uninfected T-cell line, H9. Four DNA-binding activities were observed, including non-specific DNA-binding activity and at least two activities (forms I and II) which bind specifically to a HinfI restriction fragment from nucleotides +181 to +334 relative to the transcription start site. DNA-binding activities I and II were partially resolved by ion-exchange chromatography and mapped by protection experiments to two 10-20-bp blocks surrounding the polyadenylation site at +221. Of the cell lines tested, form II was abundantly found in C10/MJ, and forms I and IV were also found in C91/PL, C81-66-45, MT2 and H9 cells.
Insights
Researchers identified specific DNA-binding proteins within the human T-cell lymphotropic virus type I (HTLV-I) long terminal repeats (LTRs). These proteins, forms I and II, bind near the polyadenylation site, potentially regulating viral gene expression.
Area of Science:
- Virology
- Molecular Biology
- Genetics
Background:
- Long terminal repeats (LTRs) of RNA tumor viruses, such as human T-cell lymphotropic virus type I (HTLV-I), are crucial for viral gene expression control.
- Sequence-specific DNA-binding proteins are hypothesized to regulate viral functions by interacting with LTRs.
Purpose of the Study:
- To identify and characterize sequence-specific DNA-binding proteins interacting with the HTLV-I LTR.
- To investigate the potential role of these proteins in regulating HTLV-I gene expression.
Main Methods:
- Utilized an in vitro non-denaturing polyacrylamide gel assay.
- Employed restriction fragments of the HTLV-I LTR and nuclear protein extracts from infected and uninfected T-cell lines.
- Performed ion-exchange chromatography and protection experiments for protein mapping.
Main Results:
- Observed four distinct DNA-binding activities, including non-specific and specific binding.
- Identified two specific DNA-binding activities (forms I and II) that bind to a HinfI fragment (+181 to +334) of the HTLV-I LTR.
- Mapped these activities to two 10-20 bp blocks surrounding the polyadenylation site (+221).
- Form II was abundant in C10/MJ cells, while forms I and IV were found in multiple cell lines.
Conclusions:
- Sequence-specific DNA-binding proteins interacting with the HTLV-I LTR, particularly near the polyadenylation site, have been identified.
- These proteins likely play a role in the regulation of HTLV-I gene expression.
- Differential expression of these binding activities across cell lines suggests cell-type-specific regulatory mechanisms.