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J. Bacteriol., 02 1995, 508-516, Vol 177, No. 3
R Li, NS Dickerson, UW Mueller and SS Golden
The psbAII gene of the cyanobacterium Synechococcus sp. strain PCC 7942 is
a member of a three-gene family that encodes the D1 protein of the
photosystem II reaction center. Transcription of psbAII is rapidly induced
when the light intensity reaching the culture increases from 125
microE.m-2.s-1 (low light) to 750 microE.m-2.s-1 (high light). The DNA
segment upstream of psbAII that corresponds to the untranslated leader of
its major transcript has enhancer activity and confers high- light
induction. We show that one or more soluble proteins from PCC 7942
specifically bind to this region of psbAII (designated the enhancer
element). In vivo footprinting showed protein binding to the enhancer
element in high-light-exposed cell samples but not in those maintained at
low light, even though in vitro mobility shifts were detectable with
extracts from low- or high-light-grown cells. When 12 bp were deleted from
the psbAII enhancer element, protein binding was impaired and high-light
induction of both transcriptional and translational psbAII-lacZ reporters
was significantly reduced. This finding indicates that protein binding to
this region is required for high-light induction of psbAII. The mutant
element also showed impaired enhancer activity when combined with a
heterologous promoter.
Copyright © 1995, American Society for Microbiology
Specific binding of Synechococcus sp. strain PCC 7942 proteins to the enhancer element of psbAII required for high-light-induced expression
Department of Biology, Texas A&M University, College Station 77843-3258.
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