Abstract
Publisher Summary This chapter discusses the covalent structural modification of DNA-dependent RNA polymerase as a means for transcriptional control exclusively with Escherichia coli . It discusses two different covalent structural modifications of DNA-dependent RNA polymerase after infection with bacteriophage T4. Two different ADP-ribosylating enzymes, one contained in the virion and the other synthesized in the infected cell, are encoded in the genome of bacteriophage T4. The virion-contained enzyme is rather unspecific. The enzyme synthesized in the infected cell is highly specific for a defined site in the RNA polymerase a-subunit. T4-modified RNA polymerase differs from normal RNA polymerase in its transcription specificity. It is strongly disturbed in its capacity to transcribed coli genes but can transcribe T4 genes normally. Thus, modification might well be a negative control mechanism helping to eliminate the competition of host transcription with phage gene expression. In addition, modification may play a positive role in the expression of certain nonearly phage genes. This latter claim, however, requires further substantiation.
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