In vitro regulation of phage lambda cII gene expression by Escherichia coli integration host factor.

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Abstract
The effect of E. coli integration host factor (IHF) on phage .lambda. gene expression was examined in a simplified DNA-directed in vitro system that measures the formation of the first dipeptide of the gene product. Plasmid pKC30cII, which contains the phage .lambda. genes N, cII and O, under control of the PL promoter, was used as template to study the expression of the first dipeptide of the gene products, i.e., fMet-Asp for N protein, fMet-Val for cII and fMet-Thr for O. Purified IHF stimulates the DNA-directed synthesis of fMet-Val (cII) and fMet-Thr (O)2- to 3-fold but has no effect on the synthesis of fMet-Asp (N). In this in vitro system, the stimulation by IHF of cII and O gene expression is at the level of transcription. Phage .lambda. repressor completely inhibits dipeptide synthesis in the presence or absence of IHF. The results are consistent with a role of IHF as a transcription antiterminator, perhaps functioning at or near the tR1 site preceding the cII gene.