No abstract

The phage T4 gene 45 protein (gp45), Escherichia coli beta and the eukaryotic proliferating cell nuclear antigen (PCNA) function in replication as processivity factors of their corresponding DNA polymerases. The T4 gp45 also functions as the transcriptional activator that connects expression of viral late genes to DNA replication. DNA tracking is an essential component of the replication and transcription regulatory functions of T4 gp45. The ability of gp45, beta and PCNA to track along DNA has been analyzed by photocrosslinking. Each of these proteins must be loaded onto DNA by a species‐specific assembly factor. For gp45 and beta, the density of traffic along DNA is determined by a dynamic balance between continuous protein loading and unloading, and is also dependent on interaction with the conjugate single‐stranded DNA binding protein.

Replication proteins encoded by bacteriophage T4 generate DNA replication forks that can pass a molecule of Escherichia coli RNA polymerase moving in the same direction as the fork in vitro. The RNA polymerase ternary transcription complex remains bound to the DNA and retains a transcription bubble after the fork passes. The by-passed ternary complex can resume faithful RNA synthesis, suggesting that the multisubunit RNA polymerase of E. coli has evolved to retain its transcript after DNA replication, allowing partially completed transcripts to be elongated into full-length RNA molecules.

No abstract

The regulation of bacteriophage T4 middle and late gene expression involves previously unrecognized mechanisms. Middle transcription requires a DNA-binding transcriptional activator and a sigma 70-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.