Comparative analysis of the in vivo and in vitro expression of bacteriophage T7 messenger RNAs during infection of Escherichia coli

Abstract

At least 20 major polypeptides encoded by the bacteriophage T7 genome have been synthesized in vitro in a protein synthesis system derived from uninfected Escherichia coli cells. Identification of these polypeptides as gene-specific products has been made by using appropriate amber and deletion mutants. The pattern of polypeptide synthesis obtained in vitro with extracted RNA has been compared to the pattern observed in vivo throughout the time-course of infection. Nearly all the identified polypeptides display a similar time-course of synthesis in vitro and in vivo. The fidelity of the in vitro pattern extends even to the relative differences in levels of synthesis among most of the various polypeptides. When the data are interpreted in terms of relative messenger RNA activities, the results indicate (1) that each of approximately two-thirds of the T7-specified mRNAs shows essentially the same time-course of translational expression in vitro as in vivo, and (2) any differences or similarities in activities among the various mRNA species, as determined late in infection, are similar in vitro and in vivo. Only a few notable exceptions to these generalities have been observed. The level of synthesis of two early proteins (products of genes 0.3 and 1) late in infection compared to early in infection is higher in vitro than in vivo. Second, the level of synthesis of one of the two gene 10-affected polypeptides (late proteins) is consistently higher in vitro compared to in vivo. These results make it unlikely that alterations in ribosomes or initiation factors play a major role in the regulation of T7 gene expression.