hetL and Anabaena PCC 7120 heterocyst development /
Prokaryotic development model systems include Bacillus subtilis sporulation, Myxococcus xanthus fruiting body formation, Caulobacter crescentus differentiation, Rhizobium symbiosis with plants, Streptomyces sporulation, and Anabaena heterocyst formation. This study focused on heterocyst development...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
2002.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=726462151&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Prokaryotic development model systems include Bacillus subtilis sporulation, Myxococcus xanthus fruiting body formation, Caulobacter crescentus differentiation, Rhizobium symbiosis with plants, Streptomyces sporulation, and Anabaena heterocyst formation. This study focused on heterocyst development in Anabaena PCC 7120. Previous studies showed that during heterocyst formation three DNA elements are excised out of the chromosome. In this study, a reporter strain was constructed to identify genes that regulate the nifD rearrangement, which is one of the three DNA rearrangements. A luxCDABE operon was inserted downstream of the nifD element in the Anabaena PCC 7120 chromosome. The reporter strain could be used to screen for mutants defective in the nifD DNA rearrangement, in nifH promoter regulation, or in heterocyst formation. The next part of the dissertation reported an effort to identify genes involved in PatS signaling. PatS-5 is a pentapeptide corresponding to the last five encoded amino acids of the patS ORF. Previous studies showed that the addition of PatS-5 in the medium or extra copies of patS in the cell suppress heterocyst formation. patS null mutant strain forms heterocysts in nitrate-containing medium. PatS is a proposed intercellular peptide signal made by heterocysts or potential heterocysts to suppress heterocyst formation in neighboring cells. In an effort to identify genes involved in PatS signaling, the hetL gene was isolated. Anabaena PCC 7120 forms heterocysts in approximately one out of ten cells along filaments under diazotrophic growth conditions. This study showed that in a patS-overexpression strain, the overexpression of hetL causes heterocyst formation. In wild-type Anabaena PCC 7120, hetL overexpression from a heterologous promoter induces multiple contiguous heterocyst development in nitrate- or ammonium-containing medium. A hetL null mutant showed normal heterocyst development and diazotrophic growth. Almost the entire amino acid sequence of the predicted HetL protein is composed of pentapeptide repeats. The consensus of the repeats is A(D/N)L*X, where * is a polar amino acid. We showed that PatS-5 is unable to suppress heterocyst formation in the hetL overexpression strain. Earlier research has shown that NtcA is required to initiate heterocyst formation. We showed that hetL overexpression caused partial heterocyst development in a ntcA null mutant. |
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| Item Description: | Vita. "Major Subject: Microbiology". |
| Physical Description: | xii, 160 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 131-157). |