Regulation of the cyanobacterial psbA genes in response to light intensity : cis-regulatory elements and their interaction with trans-acting factor(S) /
Three psba genes encoding the Dl protein of the photosystem
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| Format: | Thesis Book |
| Language: | English |
| Published: |
[Place of publication not identified] :
[publisher not identified] ;
1994.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=741965681&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Three psba genes encoding the Dl protein of the photosystem 11 reaction center are differentially expressed under different light intensities in the cyanobacterium Synechococcus sp. strain PCC 7942. When light intensity is increased from 125 liE.M-2-S-1 to 750-M-2.S-1, the expression of psbAI is reduced but that of both psbAII and psbAIII is rapidly induced. A transcriptional lacz reporter gene was developed to characterize the ciscontrolling elements of the three psba genes. The following elements were identified. Functional promoters, comparable to Escherichia Coli a7O promoters in position and sequence, confer constitutive expression of the genes under both low and high light intensities. At least two other distinct cis elements are present in the regulatory regions of psbAII and psbAIII: negative elements upstream of the promoters down-regulate the expression of the corresponding gene, and sequences downstream of the promoters that correspond to the untranslated leader regions of the mRNAs are responsible for increased expression under high light. When these light- responsive elements were combined with an E. coli promoter (conII) in different positions and orientations, the expression of the conII-lacZ gene was induced 4 to 11 fold. This is the first demonstration of enhancer elements in cyanobacteria. The high-light induction by these enhancers is position independent but orientation dependent. When the elements were combined with the conII promoter in the correct orientation, they also conferred a small but reproducible level of light-responsive expression on this E. coli promoter. Soluble proteins from Synechococcus enriched for DNA-binding activity was demonstrated to specifically bind to the psbAII enhancer and highlight-responsive DNA sequences downstream of the transcription start site. In vivo, protein binding to the upstream region of psbAII was observed only in high-light exposed cell samples but not in those maintained at low light. When 12 bp from the psbAII protein binding sites were deleted, protein binding was impaired and high-light induction of both transcriptional and translational lacz reporters was significantly reduced, indicating that the protein binding to this region is required for high-light- induced psbAII gene expression. The mutant element also showed impaired enhancer activity when combined with the heterologous E. coli conII promoter. |
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| Item Description: | Vita. "Major Subject: Biology". |
| Physical Description: | xi, 91 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references. |