Molecular events in cells transformed by Rous Sarcoma virus

Area of Science:

• Molecular Biology
• Virology
• Biochemistry

Background:

• The Rous sarcoma virus (RSV) transforming gene product, pp60src, is a 60,000 molecular weight phosphoprotein.
• pp60src possesses an associated phosphotransferase activity with a unique specificity for phosphorylating tyrosine residues.

Purpose of the Study:

• To characterize the enzymatic activity of pp60src and its relationship to the RSV transforming gene.
• To investigate the regulation of pp60src activity in transformed cells and its potential link to cyclic AMP (cAMP).

Main Methods:

• Comparison of pp60src-protein kinase activity from cells transformed by wild-type RSV versus a temperature-sensitive mutant.
• Identification of cellular proteins as substrates for pp60src kinase activity.
• Analysis of pp60src phosphorylation by cellular cAMP-dependent protein kinase.

Main Results:

• Enzymatic activity of pp60src is encoded by the RSV transforming gene, as demonstrated by differential enzyme half-lives in wild-type versus mutant transformed cells.
• pp60src phosphorylates cellular proteins in vitro and in transformed cells.
• pp60src contains a serine residue phosphorylated by cAMP-dependent protein kinase, suggesting indirect cAMP regulation.

Conclusions:

• The RSV src gene product, pp60src, functions as a tyrosine kinase, contributing to cellular transformation.
• pp60src activity may be indirectly regulated by cellular cAMP levels.
• The viral src gene is likely derived from a conserved cellular gene involved in cAMP-mediated regulatory circuits.