Old phage, new insights: Two recently recognized mechanisms of transcriptional regulation in bacteriophage T4 development

The regulation of bacteriophage T4 middle and late gene expression involves previously unrecognized mechanisms. Middle transcription requires a DNA‐binding transcriptional activator and a σ70‐binding co‐activator. The coupling of late transcription to DNA replication is effected by a DNA‐tracking protein that is loaded onto DNA by an assembly factor at enhancer‐like entry sites. Late transcription also requires an RNA polymerase core‐binding co‐activator. The co‐activators of T4 middle and late transcription share the property of depressing unactivated, basal transcription.