Cellular proteins which can specifically associate with simian virus 40 small t antigen.

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• The simian virus 40 (SV40) small t antigen is a viral protein with known roles in viral replication and cellular transformation.
• The precise biochemical functions and cellular interactions of small t antigen are not fully elucidated.
• Understanding protein-protein interactions involving viral proteins can provide insights into viral pathogenesis and cellular mechanisms.

Purpose of the Study:

• To identify cellular proteins that specifically bind to SV40 small t antigen in vitro.
• To investigate the structural requirements for the binding interaction.
• To determine the cellular localization and potential in vivo interactions of the identified binding partners.

Main Methods:

• Affinity chromatography using homogeneous simian virus 40 small t antigen-Sepharose adsorbents.
• Binding assays with radiolabeled cell extracts.
• Analysis of binding inhibition by protein modification (reduction and alkylation).
• Cell fractionation and subcellular localization studies.
• Immunoblotting and comparative partial proteolytic digestion for protein identification.
• Coimmunoprecipitation assays to assess in vivo interactions.

Main Results:

• Three cellular proteins (57, 32, and 20 kilodaltons [kDa]) specifically bound to the SV40 small t antigen-Sepharose adsorbent.
• Binding occurred with both homogeneous t antigen and a truncated t derivative, indicating a role for native conformation but not the entire primary structure.
• Binding was significantly inhibited by reduction and alkylation, suggesting dependence on specific structural elements.
• The 57-kDa protein was identified as tubulin, a major cytoskeletal component.
• The 57-kDa (tubulin) and 32-kDa proteins were localized to non-nuclear fractions, while the 20-kDa protein was associated with a nuclear fraction.
• Tubulin and small t antigen were found to coimmunoprecipitate from crude cell extracts.

Conclusions:

• SV40 small t antigen possesses a discrete in vitro biochemical function involving the specific binding of cellular proteins.
• Tubulin, a key cytoskeletal protein, is identified as a binding partner for small t antigen.
• The interaction between small t antigen and tubulin, evidenced by coimmunoprecipitation, suggests a potential in vivo association.
• These findings open avenues for exploring the role of small t antigen in cellular processes involving tubulin and the cytoskeleton.