|
Description:
|
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 . |