Transcriptional Regulation of T4 Bacteriophage-Specific Enzymes Synthesized In Vitro

Abstract

In contrast to dihydrofolate reductase and four other phage-specific enzymes, the initiation of deoxynucleotide kinase is essentially prevented if rifampin is added to a culture of Escherichia coli B cells within 1.5 min after infection with T4. Deoxynucleotide kinase thus belongs to a group of so-called delayed-early enzymes that is not initiated from an immediate-early promoter site. We prepared crude extracts from infected cells in a manner designed to maintain the integrity of the complexes of native, endogenous T4 DNA with bacterial structural and enzymatic units concerned with RNA synthesis. The initiation of the synthesis of the mRNA for dihydrofolate reductase, an example of an immediate-early enzyme, and deoxynucleotide kinase, a special type of delayed-early enzyme, was studied with these extracts prepared from cells infected in the absence or presence of chloramphenicol. Initiation of transcription of the dihydrofolate reductase gene is immediate when programmed by extracts made either from cells treated with chloramphenicol prior to infection (CM extracts) or from cells 3 min into the normal infection cycle (3-min extracts). However, initiation of transcription of the deoxynucleotide kinase gene programmed by CM extracts is delayed 2 min relative to the immediate initiation of transcription of the deoxynucleotide kinase gene programmed by 3-min extracts. These experiments duplicated in vitro effects of the antibiotics on the synthesis of phage-specific mRNA previously noted only in vivo.