Phase determination of circadian gene expression in Synechococcus elongatus PCC 7942 /
Gene expression in the cyanobacterium Synechococcus elongatus PCC 7942 is rhythmic in a circadian manner, but the phasing of peak and trough times differs among different genes. The majority of genes are designated as class 1, with expression peaks near dusk or subjective dusk (the time correspondin...
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| Format: | Thesis Book |
| Language: | English |
| Published: |
[Place of publication not identified] :
[publisher not identified] ;
2001.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=726104611&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Gene expression in the cyanobacterium Synechococcus elongatus PCC 7942 is rhythmic in a circadian manner, but the phasing of peak and trough times differs among different genes. The majority of genes are designated as class 1, with expression peaks near dusk or subjective dusk (the time corresponding to dusk in the absence of a diurnal cycle). A minority, of which purF is an example, has expression peaks approximately 12 h out of phase with class 1 genes. A screen of Tn5 mutants for those in which purF phasing is altered revealed a mutant that carries an insertion in the opcA gene. However, the expression pattern of the purF promoter is not altered by opcA inactivation, but rather the FMNHâ‚‚ substrate of luciferase is limiting at the time of the natural circadian peak. The results suggest a temporal separation of reductant-generating pathways in S. elongatus. The opcA gene, expected to be cotranscribed with fbp and zwf, was shown to have its own class 2 promoter, whereas the fbp promoter was determined to be in class 1. The purF promoter was analyzed and a functional class 2 promoter was narrowed down to 90 bp. Further dissection of this 90 bp fragment revealed that the purF promoter strength is always linked to the right phasing. No specific cis element has been found to be responsible for the right phasing. Right phasing may be the reason for the full expression of purF. A newly confirmed Tn5 mutant has an arrhythmic phenotype in class 2 reporters, but not in a class 1 kaiB::luxAB reporter. The gene that Tn5 inserted in was fully sequenced. It has high similarities to ATP dependent helicase genes. Preliminary experiments show that DNA superhelicity has opposite effect on class 1 and class 2 gene expressions. These and the data from purF promoter analysis hint the possible involvement of the DNA topology in the circadian regulation of class 2 gene expression. |
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| Item Description: | Vita. "Major Subject: Microbiology". In title numerals are used. |
| Physical Description: | x, 141 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 115-140). |