Integration host factor (IHF) represses aChlamydomonaschloroplast promoter inE.coli

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Abstract
We show that in Escherichia coli, a Chlamydomonas chloroplast promoter, PA, is repressed by Integration Host Factor (IHF). The himA42 mutation, altering the .alpha.-subunit of E. coli IHF, leads to over-accumulation of PA transcripts in vivo. This effect requires upstream chloroplast DNA sequences. DNAase I and methylation protection experiments show that IHF binds in vitro to a site within PA and band-retardation shows that IHF inhibits formation of PA-E. coli RNA polymerase open complexes. We interpret these results, together with our previously deletion analyses, to mean that in E. coli, repression of PA by IHF minimally requires both binding of IHF to a site overlapping PA and binding of one or more additional proteins, perhaps including IHF itself, to sequences upstream of PA.