Evidence for the Presence of Nontranslated T7 Late mRNA in Infected F′(PIF + ) Episome-Containing Cells

Abstract

The inability of T7 to develop in cells of Escherichia coli containing F + or substituted F′ episomes is a result of the failure to synthesize late proteins; no in vivo translation of mRNA species synthesized by the T7 RNA polymerase occurs. Further experiments have been performed to measure the amount of late mRNA in T7-infected F′(PIF + ) cells. (We have designated the property of phage inhibition of F factors as PIF; the wild-type episome is therefore F′[PIF + ].) T7 late proteins were synthesized in vitro by using a system programed with RNA extracted from T7-infected F − and F′(PIF + ) cells. The T7 lysozyme, product of gene 3.5, and the gene 10 head protein were assayed. The following results were obtained: (i) mRNA capable of supporting in vitro synthesis of lysozyme and the gene 10 head protein is present in T7-infected F′(PIF + ) cells; (ii) lysozyme mRNA extracted from T7-infected F′(PIF + ) cells is present at 70 to 75% of the level found in T7-infected F − cells; (iii) gene 10 mRNA is present at 35 to 78% of the level found in T7-infected F − cells. No in vivo synthesis of either lysozyme or gene 10 protein can be detected in T7-infected F′(PIF + ) cells although normal synthesis of these proteins occurs in F − cells. These findings confirm that the block in T7 development in F′(PIF + ) cells results from the failure to translate late classes of T7 RNA.