THE PLANT CELL, Vol 2, Issue 5 447-455, Copyright © 1990 by American Society of Plant Biologists
Spacing between GT-1 Binding Sites within a Light-Responsive Element Is Critical for Transcriptional Activity
P. M. Gilmartin and N. H. Chua
Laboratory of Plant Molecular Biology, The Rockefeller University, 1230 York Avenue, New York, New York 10021-6399
Dissection of the light-responsive element (LRE) located between -166 and
-50 of rbcS-3A from pea has revealed critical spacing requirements between
the two GT-1 binding sites for light-responsive transcription. An increase
in spacing between the two sites by as little as 2 bp reduces dramatically
the rbcS-3A transcript levels in vivo. Mutation of the 10 bp between the
binding sites leads to slightly lower transcript levels, as do deletions of
either 3 bp or 8 bp. Deletions of 5 bp or 7 bp from between the GT-1
binding sites do not affect rbcS-3A transcript levels; however, a deletion
of 10 bp virtually abolishes the activity of this element. These spacing
changes within the light-responsive element similarly affect transcription
of a divergently oriented and truncated nopaline synthase promoter. Most
spacing changes between the two GT-1 binding sites, however, do not impair
the binding of GT-1 to this element in vitro. Together with previous
observations, these results suggest that the nuclear factor GT-1 may
interact with the binding sites in either a productive or nonproductive
manner and that GT-1 binding is necessary but not sufficient for
light-responsive transcription. We also discuss our results in relation to
the observed spacing of similar sequence elements present within other
light-responsive promoters.
