Regulation of a new bacteriophage T4 gene, 69, that spans an origin of DNA replication.

We have determined the DNA sequence and transcription patterns in a 3-kb segment (between 15 and 18 kb on the standard phage T4 map) spanning an origin of DNA replication. A new gene, 69, spans this origin. Gene 69 codes for two overlapping proteins that share a common C-terminal segment. Defective DNA replication in an appropriate amber mutant shows that at least the larger of the two proteins is required for efficient T4 DNA replication. The two proteins coded by gene 69 are expressed from different transcripts that are under different regulation. The smaller protein, gp69*, can be expressed immediately from an Escherichia coli-like promoter, whereas expression of the larger protein, gp69, must be delayed since its middle promoter requires T4 coded proteins, most likely gp mot, for activation. We discuss the possible significance of two overlapping proteins in the assembly of replisomes. Gene 69 is bracketed by the non-essential early gene dam (DNA adenine methylase) and the late gene soc (small outer capsid protein). Transcripts through this region are interdigitated in a complex pattern, which reveals all elements that are thought to be important in regulation of pre-replicative and post-replicative T4 genes.