Identification of an UP element within the IHF binding site at the P(L)1-P(L)2 tandem promoter of bacteriophage lambda

An UP element defines a supplementary promoter element located upstream of the -35 region that stimulates transcription by interacting with the C-terminal domain of the RNA polymerase alpha subunit (alpha CTD). The alpha CTD also responds to various transcription activators, including the integration host factor protein, MF, in the stimulation of the bacteriophage lambda P-L promoter. P-L consists Of-the tandem P(L)1-P(L)2 promoters where P(L)1 is stimulated and P(L)2 is repressed by IHF. We identified a functional UP element that binds the alpha subunit of RNA polymerase and is located in the region from -36 to -60 relative to the P(L)2 start site. P(L)2 expression requires the presence of the UP element and requires an intact alpha CTD. The UP element is nested within the DNA region protected by IHF against DNase I digestion. We used mutational analysis to identify the MF recognition sequence which was found to be located downstream of the UP element, overlapping the -35 region of P(L)2. The possible function of the complex structure of the P-L promoter is discussed. (C) 1996 Academic Press Limited