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’ gene^2,3, 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 proven^4,5. Furthermore, we have previously shown that T7 early mRNAs are functionally unstable, although they remain chemically stable late in T7 infection^6,7. 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.