Simian virus 40 gene A function and maintenance of transformation

Area of Science:

• Virology
• Molecular Biology
• Cell Biology

Background:

• Simian virus 40 (SV40) is a DNA tumor virus known to induce tumors in various animal species.
• SV40-induced transformation of cells involves alterations in cellular growth properties and morphology.
• Temperature-sensitive mutants of SV40 provide valuable tools for studying viral gene functions.

Purpose of the Study:

• To investigate the role of the SV40 A function in maintaining the transformed phenotype of rat embryo cells.
• To determine the temperature dependence of transformation-associated properties in SV40-infected cells.
• To elucidate the relationship between A function activity, T-antigen expression, and cellular transformation.

Main Methods:

• Infection of rat embryo cells with wild-type SV40 and temperature-sensitive mutants (tsA7, tsA28).
• Assessment of transformation-associated phenotypes: growth in low serum, growth rate, saturation density, and cell morphology.
• Evaluation of T-antigen expression in infected cells.
• Temperature shift experiments to assess phenotype reversibility.

Main Results:

• Cells transformed by tsA mutants exhibited temperature-dependent transformation properties, including growth and morphology.
• Wild-type SV40 transformants showed temperature-independent transformation characteristics.
• T-antigen expression was also found to be temperature-dependent in tsA transformants.
• Reversibility of the transformed phenotype upon temperature shift indicated a requirement for active A function.

Conclusions:

• The SV40 A function is essential for the maintenance of cellular transformation.
• Transformation by SV40 may result from the continuous activity of the viral DNA replicon and its initiator function.
• The viral A function's role in initiating DNA synthesis during the lytic cycle is linked to its ability to induce a transformed phenotype.