Isolation of an inhibitor protein of E. coli RNA polymerase from T7 phage infected cell.

Abstract

BACTERIOPHAGE T7 gene expression is under a unique transcriptional control. The ‘early to late’ switch in T7 development involves a switch from the host Escherichia coli RNA polymerase to the T7-coded enzyme (T7-specific RNA polymerase1), transcribing early mRNA and late mRNA, respectively, from two different regions of the T7 genome2. In addition to the gene 1 coding for T7-specific RNA polymerase, this early–late switch requires the function of another early gene of T7, gene 0.7 or the ‘host shut-off’ gene2,3, to shut off the synthesis of host RNA and T7 early mRNA. This shut-off function is assumed to be an inactivation of the host RNA polymerase, although this has not been proven4,5. Furthermore, we have previously shown that T7 early mRNAs are functionally unstable, although they remain chemically stable late in T7 infection6,7. Thus, it seems that a complete switch of T7 gene expression from early to late involves at least three different control mechanisms. It has been shown that a T7-coded translational repressor may also play a role in the elimination of host functions8.