Programmed DNA rearrangements and suppression of heterocysts in Anabaena sp. strain PCC 7120 /
Anabaena sp. strain PCC 7120 undergoes three programmed DNA rearrangements during the differentiation of heterocysts. Here we describe the identification and characterization of genes necessary for the rearrangement of the 55-kb fdxN element. We show that rearrangement of the fdxN element requires...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1997.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=739887851&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Anabaena sp. strain PCC 7120 undergoes three programmed DNA rearrangements during the differentiation of heterocysts. Here we describe the identification and characterization of genes necessary for the rearrangement of the 55-kb fdxN element. We show that rearrangement of the fdxN element requires the recombinase XisF. Inactivation of xisF blocks the excision of the fdxN element. The cloned xisF gene is sufficient to cause site-specific rearrangement of an artificial substrate in Escherichia coli. Forced transcription of xisF in vegetative cells did not result in excision of the fdxN element suggesting that other factors may be involved in cell-type specificity. The predicted XisF protein shows similarity to members of the resolvase family of recombinases. We also show the requirement of two overlapping genes xisHI for the heterocyst specific rearrangement of the fdxN element. Deletion of a 3.2-kb region downstream of the xisF gene blocked the fdxN element rearrangement in heterocysts. The 3.2-kb deletion was complemented by xisH and xisI. Interestingly, extra copies of xisH and xisI on a replicating plasmid resulted in the xisF dependent excision of the fdxN element in vegetative cells. Therefore, xisHI are involved in the control of cell- type specificity of the fdxN rearrangement. The xisHI- induced excision of the fdxN element produced strains lacking the element and demonstrates that the 55-kb element no essential genes. xisH and xisI do not show similarity to any other known genes. Mutants of Anabaena sp. strain PCC contains 7120 that formed heterocysts on nitrate-containing media were isolated in our effort to identify genes that affect heterocyst development. Characterization of the mutant strain AMC260, which forms 6-8% heterocysts on nitrate containing media, is presented. A 1.2-kb moeA gene complemented the AMC260 mutant. The predicted Anabaena sp. strain PCC 7120 MoeA polypeptide shows 37% identity to MoeA from Escherichia coli, which is required for molybdopterin biosynthesis. Molybdopterin is required by all molybdoenzymes such as nitrate reductase. We show that AMC260 lacks methyl viologen supported nitrate reductase activity and conclude that the inability of AMC260 to metabolize nitrate results in the formation of heterocysts on nitrate containing media. |
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| Item Description: | Vita. "Major Subject: Microbiology". In title, numerals and symbols are used. |
| Physical Description: | x, 131 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references: pages 112-128. |