Light-responsive expression of the psbA and psbD gene families in Synechococcus sp. strain PCC 7942 /
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1991.
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| Subjects: | |
| Online Access: | Link to OAKTrust copy |
| Abstract: | The genome of the cyanobacterium Synechococcus sp. strain PCC 7942 contains three psbA genes and two psbD genes which encode the D1 and D2 proteins of the photosystem II reaction center. Each of the psbA genes produces a 1.2 kb mRNA. We investigated the effect of changes in light intensity on psbAII transcript levels in a series of light-shift experiments in wild-type Synechococcus. After exposure to high light intensities for 15 minutes, the levels of 1.2 kb psbAII and psbAIII transcripts increased 500%; however; these transcripts were not detected after transfer to low light intensity. The psbAI transcript levels responded oppositely to those of psbAII and psbAIII, whereas the 1.6 kb psbAII mRNA was unaffected by different light intensities. In the psbD family, the psbDI gene is cotranscribed with psbC (the gene for CP43, a chlorophyll a-binding protein), producing a dicistronic message; the other member, psbDII, is monocistronic. Northern-blot analysis of psbD transcripts showed that the two genes respond differently when wild-type cells are shifted from moderate to high light intensities: psbDII transcripts increased 500% whereas psbDI-psbC transcripts remained constant. D2 protein levels in thylakoid membranes from wild-type cells increased to 250% of unshifted control cells 12 h after a shift to high light. In contrast, in a mutant strain (AMC016) that carries an inactive psbDII gene, D2 levels decreased by 50% under identical conditions. Soluble proteins from Synechococcus cells shifted to high light and enriched for DNA-binding proteins were found to have affinity for the psbDII upstream region. DNA mobility shift and copper-phenanthroline footprinting assays of a 258 bp psbDII upstream fragment revealed three distinct DNA-protein complexes that mapped to the 5' untranslated region from +10 to +82 relative to the transcriptional start site. A 4 bp deletion within the promoter-proximal protected region decreased p-galactosidase activity to approximately 2% of the undeleted control; however, the gene remained light-responsive. Deletion of the three protected regions completely abolished gene expression and light induction. These results suggest that the psbDII gene requires additional elements within the untranslated region for efficient gene expression; one of these elements may be involved in light-responsive regulation. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Biology." |
| Physical Description: | xi, 113 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |