Formation of RNA in T4 phage-infected bacteria: Transcriptional regulation of early enzyme synthesis

Abstract

The rates of synthesis were determined for those early mRNA species which code for early enzymes involved in phage-specific DNA synthesis. Evidence was found for a regulation mechanism which specifically restricts the transcription of early genes. The formation of early mRNA representing certain early genes was measured at different times after infection by phenotypic suppression by 5-fluorouracil of amber mutations in the early genes 1 (hydroxymethyl deoxycytidylate kinase), 42 (deoxycytidylate hydroxymethylase), and 56 (deoxycytidine triphosphatase), respectively. Suppression was measured by the determination of DNA synthesis and phage production. Since 5-fluorouracil suppression of amber mutations is effected by the incorporation of the analog into mRNA, the relative efficiency of suppression at different times after infection was interpreted to reflect the rate of mRNA formation at the time of fluorouracil addition. The regulation of early mRNA synthesis was also directly demonstrated by short-time labeling with uracil- 3H and fluorouracil- 3H after the infection of E. coli B with the mentioned phage mutants, which are DNA negative and produce no late mRNA. The uptake of 5-fluorouracil as an RNA precursor into the ribonucleotide pools of the infected cell was checked by electrophoretic analysis at different times after infection.