Abstract
ne PsbAII gene Of Synechococcus Sp. strain PCC 7942 is a member of a small gene family encoding the DI Protein found in the photosystem R reaction center. Previous studies have shown that expression of the psbAII gene is regulated in response to changes in light intensity. Low levels of expression are observed under low-light conditions, and expression increases with increasing light intensity. DNA mobility shift assays using soluble protein extracts isolated from Synechococcus cells grown under high-light conditions indicate that two proteins bind to sequences located within the promoter region of the psbAII gene. DNA mobility shift assays and competion assays using small DNA fragments containing portions of the psbAII promoter region have localized DNA sequences required for protein binding to the regions of +7 to +17 and +25 to +29. Deletion of DNA sequences near these regions reduced the level of protein binding as compared to the wild-type promoter fragment. The role of protein binding in light regulated gene expression was examined by testing the ability of psbAII derived promoter fragments to drive the expression of the Escherichia coli lacz gene in Synechococcus cells grown under low-and high-light conditions. The promoter fragments used to create these reporter constructs showed different levels of protein binding in DNA mobility shift assays. Reduction in the levels of protein binding as a result of deletions within the promoter region also reduced the level of gene expression at high-light intensity, and there appeared to be a direct correlation between the level of protein binding and gene expression. Competition assays with psbAII and other member of the psba and psbd gene families (encoding the D I and D2 proteins of photosystem II, respectively) indicated that the light-responsive members of these gene families, psbAI, psbAII, psbAIII, and psbDII, bind similar proteins and may share a common means of regulation.
Dickerson, Naoma Suzanne (1994). Characterization of protein binding to the psbAII promoter region in Synechococcus sp. strain PCC 7942 and its role in light regulated gene expression. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1994 -THESIS -D5496.