Schematic representation of the barley
chloroplast psbD BLRP. A, The top portion of the figure
shows the location of the AAG-box and PGT-box present upstream of the
psbD transcription initiation site (marked by an open
arrow and designated +1). The psbD open reading frame is
shown at the far right. The double-headed arrows represent DNA
fragments from the psbD light-responsive promoter used
for gel-retardation and competition-binding experiments. GT30 and LRP20
represent four (4X) and three (3X) tandem copies of each region
indicated in the figure. B, Gel-shift assays using a GT30 tetramer
(lane 1) or the LRP136 DNA fragment (lane 2). All gel-shift assays
contained 1 μg of poly (dI–dC)·(dI–dC). Gel-shift complexes A to
E and I to III are noted. Band D was previously identified as an AGF,
which binds specifically to the AAG-box shown in A. C, Gel-shift assays
using the radiolabeled tetramer of GT30 and various amounts (100–200
ng) of unlabeled LRP136, GT30, or LRP20 DNA. The migration of complexes
I, II, and III and the free probe is indicated. No Comp., No
competitor.