Photoregulated gene expression may involve ubiquitous DNA binding proteins.

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Abstract
Several promoter elements have previously been shown to influence the expression of the cab‐E gene in Nicotiana plumbaginifolia. Here we demonstrate, by electrophoretic mobility shift and methylation interference assays, that a complex pattern of protein‐DNA interactions characterizes this promoter. Among the multiple proteins identified, we focused on five different factors which either occupied important regulatory elements and/or were present in relatively large amounts in nuclear extracts. All of these proteins were distinguished on the basis of their recognition sequence and other biochemical parameters. One, GBF, interacted with a single sequence within the cab‐E promoter homologous to the G‐box found in many photoregulated and other plant promoters. A second factor, GA‐1, bound to the GATA element which is located between the CAAT and TATA boxes of the cab‐E and all other LHCII Type I CAB promoters. GA‐1 also interacted in vitro with the I‐boxes of the Arabidopsis rbcS‐1A promoter and the as‐2 site of the CaMV 35S promoter. Two other factors, GC‐1 and AT‐1, bound to multiple recognition sites localized within the GC‐rich and AT‐rich elements, respectively. GT‐1, a protein which interacts with promoters of other light‐regulated genes, bound to seven distinct sites distributed throughout the cab‐E promoter.