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Molecular cloning and sequencing of the MTV-1 LTR: evidence for a LTR sequence alteration
1Department of Microbiology and Immunology, University of Miami School of Medicine, FL 33101.
Abstract:
The vertically transmitted Mtv-1 provirus is the primary causative factor of mammary neoplasia in certain C3Hf strains that lack the horizontally transmitted mouse mammary tumor virus (MMTV). The studies here report the molecular cloning of the germ line 4.5 kb Mtv-1 3' EcoRI fragment and sequencing of the 3' Mtv-1 LTR. The Mtv-1 LTR sequence is closely related to the 5' Mtv-11 LTR sequence also reported here, as well as to known Mtv-8 and MMTV LTR sequences in the portion of MMTV and Mtv-8 LTRs previously demonstrated to contain transcriptional regulatory sequences. A 91 bp unique sequence region, Mtv-1 bp 862 to 952, exists in the Mtv-1 LTR, which is upstream of the sequence homology with the MMTV transcriptional regulatory domain. The Mtv-1 unique sequence region is distinct from a 117 bp sequence, bp 862 to 978, in the Mtv-11 LTR sequence as well as reported Mtv-8 and MMTV LTR sequences, and is present in the germ line Mtv-1 5' and 3' LTR-containing restriction fragments. S1 nuclease mapping experiments of C3Hf/Se mammary tumor poly(A) RNA with the cloned Mtv-1 and Mtv-11 LTRs exhibited a specific set of S1 protected fragments demonstrating that Mtv transcripts which accumulate in C3Hf spontaneous mammary tumors are encoded by the Mtv-1 provirus.
Insights
The Mtv-1 provirus causes mammary tumors in mice lacking MMTV. Researchers cloned and sequenced Mtv-1, revealing unique regulatory regions and confirming its role in spontaneous mammary tumors.
Area of Science:
- Virology
- Oncology
- Genetics
Background:
- The Mtv-1 provirus is a key cause of mammary neoplasia in specific mouse strains.
- These strains lack the horizontally transmitted mouse mammary tumor virus (MMTV).
Purpose of the Study:
- To molecularly clone and sequence the Mtv-1 provirus's 3' long terminal repeat (LTR).
- To investigate the transcriptional origin of Mtv transcripts in spontaneous mammary tumors.
Main Methods:
- Molecular cloning of the Mtv-1 3' EcoRI fragment.
- DNA sequencing of the Mtv-1 3' LTR.
- S1 nuclease mapping of mammary tumor poly(A) RNA.
Main Results:
- The Mtv-1 LTR sequence shares homology with Mtv-8 and MMTV LTRs, containing regulatory elements.
- A unique 91 bp sequence region was identified in the Mtv-1 LTR, upstream of conserved domains.
- S1 nuclease mapping confirmed that Mtv transcripts in tumors are encoded by the Mtv-1 provirus.
Conclusions:
- The Mtv-1 provirus is the source of Mtv transcripts accumulating in C3Hf spontaneous mammary tumors.
- The identified unique sequence in the Mtv-1 LTR may play a role in its specific regulation.