Characterization of Rous sarcoma virus sequences essential for viral gene expression

Area of Science:

• Molecular Biology
• Virology
• Gene Regulation

Background:

• Understanding Rous sarcoma virus (RSV) gene expression is vital for avian cell biology.
• The lacZ gene from Escherichia coli, encoding beta-galactosidase, serves as a reporter for gene expression analysis.

Purpose of the Study:

• To identify sequences essential for RSV genome expression in avian cells.
• To investigate the role of the long terminal repeat (LTR) and leader regions in directing gene expression.

Main Methods:

• Utilized the beta-galactosidase reporter system to quantify gene expression.
• Analyzed the function of RSV LTR sequences, including U3 and 3' LTR domains, in directing gag-lacZ fusion protein synthesis.
• Assessed the impact of LTR orientation and proximity to the cap site on gene expression.

Main Results:

• The RSV LTR and leader region were sufficient for high-level gag-lacZ fusion protein production.
• A U3 region element upstream of the cap site was essential for gene expression, functioning in either orientation but sensitive to distance.
• 3' LTR insertions enhanced gag-lacZ expression by increasing stable transcript levels and could compensate for 5' LTR defects.
• At least three synergistic domains within the 3' LTR were identified, influencing gene expression, particularly when adjacent to the 3'-untranslated region.

Conclusions:

• RSV LTRs interact complexly to promote high levels of stable transcripts.
• RSV gene expression in avian cells is largely independent of viral gene products, indicating limited trans-activation.
• The findings provide insights into the regulatory mechanisms governing retroviral gene expression.