Unicellular freshwater cyanobacterium Synechococcus elongatus PCC 7942 is the model
organism for studying the circadian clock in cyanobacteria. Despite tremendous work
over the last decade in identification of clock-related loci and elucidation of molecular
mechanisms of the central oscillator, many details of the basic steps in generating
circadian rhythms of biological processes remain unsolved and many components are
still missing. A transposon-mediated mutagenesis and sequencing strategy has been
adopted to disrupt essentially every locus in the genome so as to identify all of the loci
that are involved in clock function.
The complete genome sequence has been determined by a combination of
shotgun sequences and transposon-mediated sequences. The S. elongatus PCC 7942
genome is 2,695,903 bp in length, and has a 55.5% GC content. Automated annotation
identified 2,856 protein-coding genes and 51 RNA coding loci. A system for community
refinement of the annotation was established. Organization and characteristic features of
the genome are discussed in this dissertation. More than 95% of the PCC 7942 genome has been mutagenized and mutants
affected in approximately 30% of loci have been screened for defects in circadian
function. Approximately 70 new clock loci that belong to different functional categories
have been discovered through a team effort. Additionally, functional analysis of
insertion mutants revealed that the Type-IV pilus assembly protein PilN and the RNA
chaperon Hfq are involved in transformation competence of S. elongatus cells.
Functional analysis of an atypical short period kaiA insertional mutant showed
that the short period phenotype is caused mainly by the truncation of KaiA by three
amino acid residues. The interaction between KaiC and the truncated KaiA is weakened
as shown by fluorescence anisotropy analysis.
Deletion analysis of pANL, the large endogenous plasmid, implies that two
toxin-antitoxin cassettes were responsible for inability to cure cells of this plasmid.
In summary, the results indicate that this functional genomics project is very
promising toward fulfilling our goal to assemble a comprehensive view of the
cyanobacterial circadian clock. The mutagenesis reagents and dataset generated in this
project will also benefit the greater scientific community.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1552 |
| Date | 15 May 2009 |
| Creators | Chen, You |
| Contributors | Golden, Susan S. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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