Expression of the PDGF-related transforming protein of simian sarcoma virus in E. coli

The transforming gene of simian sarcoma virus (SSV), an acute transforming retrovirus, and human platelet-derived growth factor (PDGF), a potent mitogen for connective tissue cells, appear to have arisen from the same or very closely related cellular genes. In an effort to obtain sufficient quantities of the SSV transforming gene product for the detailed analysis of its structural and biologic properties, we placed the v-sis gene under the control of strong phage transcriptional and translational signals that provide for regulated expression of cloned genes in E. coli. When induced, the bacterial cells synthesized levels of the SSV transforming gene product that constituted at least 10% of their total protein. Differences in the structure and processing of the v-sis gene product in procaryotic and eucaryotic cells provided important insights concerning posttranslational modifications of this PDGF-related transforming protein in eucaryotic cells.