Roles for group 2 sigma factors in light response and circadian regulation in S. elongatus PCC 7942 /
Synechococcus elongatus PCC 7942 is a unicellular, photoautotrophic cyanobacterium that exhibits circadian rhythms of gene expression. Light environment and the circadian clock are known to regulate the expression of the psbAI gene, which encodes the D1 protein of the photosystem II reaction center....
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
2001.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=725912161&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Synechococcus elongatus PCC 7942 is a unicellular, photoautotrophic cyanobacterium that exhibits circadian rhythms of gene expression. Light environment and the circadian clock are known to regulate the expression of the psbAI gene, which encodes the D1 protein of the photosystem II reaction center. Expression of psbAI is downregulated under high light. In addition to the well-characterized degradation of the psbAI message, promoter activity decreases upon exposure to high light. The shortest fragment of the psbAI upstream region that allowed expression of a lacZ reporter extends from -54 to +1. Electrophoretic mobility shift assays showed that the DNA sequence corresponding to the untranslated leader of the psbAI message binds one or more proteins from an S. elongatus extract. The corresponding region of psbAII efficiently competed for this binding activity, suggesting a shared regulatory factor among these disparately regulated genes. Mutagenizing the -10 element from TCTCCT to TATAAT increased the magnitude of expression from both psbAI::lacZ and psbAI::luxAB fusions but did not affect the response to high light. Inactivation of group 2 sigma factor genes rpoD2 and sigC, in both wild-type and -10-element muatagenized backgrounds, resulted in elevated psbAI::luxAB expression but did not alter the downregulation at high light. The second project comprehensively analyzes the role the four group 2 sigma factors, rpoD2, rpoD3, rpoD4 and sigC, on circadian gene expression. Because the expression of the whole genome of S. elongatus is under the control of the circadian clock, one hypothesis is that clock information is conveyed from the oscillator to downstream genes via the transcriptional machinery and in part through the group 2 sigma factors. Our data suggest that the family of non-essential group 2 sigma factors contributes to circadian gene expression. Mutant phenotypes further indicate that the promoter specificities of the sigma factors are overlapping but not entirely redundant. Inactivation of the sigC gene causes a lengthening of circadian period from a subset of genes that includes the psbAI gene but does not the period of kaiB and purF expression to the same extent. These data indicate that separate timing circuits with different periods can co-exist in the cell. Both of the periods in a sigC genetic background are dependent on the period dictated by alleles of the kai genes. |
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| Item Description: | Vita. "Major Subject: Microbiology". |
| Physical Description: | x, 154 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 128-149). |