Differential response of Synechococcus psbA genes to high light intensity : mRNA regulation and functional significance /
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1994.
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| Subjects: | |
| Online Access: | Link to OAKTrust copy ProQuest, Abstract |
| Abstract: | The psbA gene family in Synechococcus sp. strain PCC 7942 encodes two distinct forms of the D1 protein of photosystem II: psbAI encodes Form I whereas psbAII and psbAIII both encode Form II. Upon exposure of cells to high light intensity the psbAI message level decays while psbAII and psbAIII message levels increase rapidly. We examined the potential contributions of transcriptional and post-transcriptional processes in this high-light response. We also studied the consequences of psbA expression during adaptation of the cells to high light. The increases in psbAII and psbAIII transcripts were due to transcriptional induction of these genes and not due to message stabilization. The disappearance of psbAI transcript was because of accelerated degradation. De novo synthesis of a factor was essential for the post-transcriptional response since blocking transcription or translation reduced the rate of decay of psbAI transcript. When transcription was blocked subsequent to the light shift rather than before allowing transcription and translation to take place, both psbAI and psbAIII messages decayed at a faster rate. psbAIII transcript levels increased to higher levels than normal when translation was blocked, consistent with susceptibility of psbAIII transcript to the high-light-induced factor. Heat shock and oxidative stress did not produce the high-light psbA response, indicating that the high-light psbA expression is a specific (and not a generalized stress) response. The long-term response to high light was characterized by elevated levels of all the psbA transcripts. Recovery of the psbAI transcript following its initial decline occurred due to stabilization of the message. The total D1 protein levels were not significantly altered, which implies that the increased synthesis may compensate for the known high-light turnover of D1. However Form II replaced Form I in the membrane at high light. Form II-encoding transcripts were enriched relative to the Form I-encoding transcript and the turnover of Form I was faster than that of Form II. Growth of a mutant which produced only Form I was impaired at high light. We propose that Form II is less susceptible to damage at high light, and that this qualitative alteration, coupled with increased turnover of D1, protects the cells from photoinhibition. |
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| Item Description: | "Major subject: Microbiology." Vita. |
| Physical Description: | xi, 95 leaves : illustrations ; 28 cm |
| Bibliography: | Includes bibliographical references. |