Abstract
1
After infection with bacteriophage T4 the DNA‐dependent RNA polymerase of the Escherichia coli host is changed in two consecutive steps: alteration and modification.
The alteration takes place immediately after phage adsorption and is independent of protein synthesis. It leads to the shut off of E. coli specific RNA synthesis and permits the transcription of the immediate early phage genes.
Under conditions allowing phage specific protein synthesis the E. coli core polymerase is modified. The first step of modification is completed within 4 min after phage infection (25°C). The purified modified enzyme does not contain σ‐factor and exhibits structural changes in all the subunits of the core.
2
Under conditions which do not allow DNA synthesis (infection with T4 am N82) the net rate in vivo of immediate early, followed by delayed early gene transcription shows one early burst.
In normal phage development immediate early and delayed early transcription display a second rise preceding replication. Late RNA is made after the onset of DNA synthesis.
3
In crude extracts prepared from E. coli cells infected under conditions which allow as well as under conditions which do not allow protein synthesis, one burst of transcriptional capacity follows infection. The length of this burst is sufficient for the transcription of approximately one reading unit. Although transcription in vivo continues under conditions allowing protein synthesis, polymerase activity in crude extracts in vitro is very low after the burst even when exogenous template DNA is added.