TRANSCRIPTION OF A REPRESSED GENE: EVIDENCE THAT IT REQUIRES DNA REPLICATION.

It is known that the synthesis of DNA is not essential for constitutive or induced enzyme synthesis. Our studies indicate that DNA synthesis is required for the basal level synthesis (that is, for synthesis in absence of inducer) of two inducible enzymes, a finding which supports an earlier speculation that a messenger-RNA transcription event may normally accompany DNA replication. Studies with cultures of Escherichia coli TAU-bar in which DNA replication is synchronized suggest that the beta-galactosidase gene is transcribed at a particular time in the sequential replication of the bacterial chromosome.