A cII-dependent promoter is located within the Q gene of bacteriophage lambda.

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Abstract
A cII-dependent promoter, PaQ, was found within the Q gene of bacteriophage .lambda.. Transcription experiments and abortive initiation assays performed in vitro showed that the promoter strength and the cII affinity of PaQ were comparable to the other cII-dependent .lambda. promoters, PE and PI. The location and leftward direction of PaQ suggests a possible role in the delay of .lambda. late-gene expression by cII protein, a phenomenon that has been called cII-dependent inhibition. We have constructed a promoter down mutation, paq-1, by changing a single base pair in the putative cII binding site of the promoter by oligonucleotide site-directed mutagenesis. The paq-1 mutant promoter required about 4-fold higher cII concentrations for maximal activation compared to the wild-type PaQ. The hypothesis that PaQ is responsible in part for the delay of .lambda. late-gene expression by recombining the paq-1 mutation into a phage showing severe cII-dependent inhibition was tested. The paq-1 mutation relieved the cII-dependent growth defect of this phage. The paq-1 mutation (in combination with .lambda. c1857) resulted in a clear-plaque phenotype at the permissive temperature of 32.degree. C. The role of the PaQ-initiated antisense transcript in the control of .lambda. development is discussed.