T7 Protein Synthesis in F′ Episome-Containing Cells: Assignment of Specific Proteins to Three Translational Groups

Abstract

Synthesis of many T7 proteins is prevented in F′ episome-containing cells. In order to quantitate the degree of inhibition, we measured the activity of several T7 proteins in extracts prepared from T7-infected F − and F′ cells and cells containing F factors mutant in phage inhibition [F′(PIF − 2A) and F′(PIF − 2A,2B)]. In addition, we were able to assign specific T7 proteins to the three translational units previously defined by polyacrylamide gel analysis of T7 proteins made in F − and episome-containing cells. After T7 infection, the presence of the wild-type F′ (PIF + ) episome led to greater than 90% inhibition of T7 DNA polymerase (product of gene 5), T7 lysozyme (gene 3.5), and gene 10 capsid protein synthesis. Nearly normal amounts of T7 RNA polymerase (gene 1) were made in these cells. T7 infection of cells containing the mutant F′ (PIF − 2A) episome led to normal synthesis of T7 RNA polymerase and T7 DNA polymerase; T7 lysozyme was synthesized at 30% of the maximal level in these cells; T7 gene 10 capsid protein synthesis was inhibited by 90%, and T7 DNA synthesis was arrested in these cells. T7 infection of cells containing the mutant F′ (PIF − 2A,2B) episome led to synthesis of normal levels of the enzymes assayed.