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Sequences in the long terminal repeats of the Moloney murine sarcoma virus-124 genome which control transforming gene
Abstract:
The role of long terminal repeat (LTR) sequences in the efficient expression of Moloney murine sarcoma virus (MSV-124) transforming gene function was investigated. Recombinant plasmids containing a single LTR positioned 3' of v-mos were subjected to sequential deletions, and the relative transforming efficiency of these recombinants was analyzed in the NIH/3T3 transfection assay. Recombinants lacking CAAT, TATA, and poly(A) signals within the LTR were able to transform with an efficiency comparable to that of the wild-type MSV-124 genome. Deletion of one of the two 74-bp tandem repeat units within the LTR did not abolish v-mos gene function, whereas removal of both 74-bp repeat units completely eliminated transforming activity. The addition of a fragment containing only a single 74-bp unit and 29-bp downstream sequences derived from the LTR to a position 3' of v-mos led to efficient activation of v-mos transforming function. Residual potentiating activity for v-mos expression was retained even when the distance between v-mos and the 3' LTR was increased by several kilobase pairs. All these findings are consistent with the concept that the potentiating action of the LTR in its 3' position is due to activator/enhancer sequences localized to one of its 74-bp repeats. A permuted MSV-124 molecule, whose single LTR was localized 5' of v-mos, was very inefficient at transformation. However, its transforming activity could be increased by approximately 1000-fold by tandemization of the molecule.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Moloney murine sarcoma virus (MSV-124) long terminal repeat (LTR) sequences enhance gene expression. A specific 74-bp repeat within the LTR is crucial for v-mos transforming activity, acting as an enhancer element.
Area of Science:
- Molecular Biology
- Virology
- Gene Expression
Background:
- Moloney murine sarcoma virus (MSV-124) is a retrovirus known for its transforming gene, v-mos.
- Long terminal repeat (LTR) sequences are critical regulatory elements in retroviral genomes.
- The precise role of LTR sequences in regulating v-mos transforming gene function requires detailed investigation.
Purpose of the Study:
- To elucidate the function of Moloney murine sarcoma virus (MSV-124) long terminal repeat (LTR) sequences in v-mos transforming gene expression.
- To identify specific regions within the LTR responsible for potentiating viral transformation.
- To understand the impact of LTR orientation and LTR sequence modifications on viral transforming efficiency.
Main Methods:
- Construction of recombinant plasmids with sequential LTR deletions.
- Analysis of relative transforming efficiency using NIH/3T3 transfection assays.
- Investigation of the role of specific LTR components like CAAT, TATA, poly(A) signals, and 74-bp tandem repeats.
Main Results:
- Recombinants lacking CAAT, TATA, and poly(A) signals retained high transforming efficiency.
- Deletion of one 74-bp repeat unit partially reduced, while deletion of both abolished, v-mos transforming activity.
- A single 74-bp repeat with downstream sequences, positioned 3' of v-mos, efficiently activated transforming function.
- Potentiating activity was retained even with increased distance between v-mos and the 3' LTR.
- A permuted MSV-124 molecule (LTR 5' of v-mos) showed low transforming activity, significantly increased by tandemization.
Conclusions:
- The potentiating action of the 3' LTR on v-mos expression is mediated by activator/enhancer sequences located within one of its 74-bp repeats.
- The orientation and precise arrangement of LTR elements significantly influence viral transforming efficiency.
- Specific repeat units within the LTR are essential for robust v-mos gene function and viral transformation.