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|Title:||Identification and regulation of genes involved in carbon dioxide fixation in Rhodobacter sphaeroides|
|Author(s):||Hallenbeck, Paul Leon|
|Doctoral Committee Chair(s):||Kaplan, Samuel|
|Department / Program:||Microbiology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||A region of DNA from the genome of the photoheterotrophic bacterium, Rhodobacter sphaeroides, was shown to contain several genes involved in CO$\sb2$ fixation, namely fructose 1,6-bisphosphatase (fbpA), phosphoribulokinase (prkA), a 37-kDa polypeptide (designed CFX A) with a putative regulatory role (cfxA), and Form I ribulose 1,5-bisphosphate carboxylase/oxygenase (rbcL,S).
The prkA gene was localized and identified by expression of the prkA gene product in vivo and in vitro. The PRK activity expressed in Escherichia coli was characterized, the product of the reaction identified chemically, and the prkA gene product expressed was identical to the gene product produced in Rb. sphaeroides.
The fbpA and rbcL,S genes were identified and localized by comparing the amino acid sequences deduced from the DNA sequence analysis with the amino acid sequence of known Fbp and RbcL proteins. These genes are all transcribed in the same direction and are tandomly arranged.
A second region of the genome contained a non-identical but similar duplicate set of these genes, namely, fbpB, prkB, cfxB and rbcR but had 3 kb of DNA between the 3$\sp\prime$ end of prkB and the 5$\sp\prime$ end of cfxB, a portion of which codes for glyceraldehyde 3-phosphate dehydrogenase (gapB).
Strains were constructed which contained null mutations in cfxA and/or cfxB. Each mutation eliminated downstream rbc expression. Studies utilizing these strains demonstrated that each form of ribulose 1,5-bisphosphate carboxylase/oxygenase plays an essential role in maintaining the cellular redox balance during photoheterotrophic growth at differing CO$\sb2$ concentrations.
Strains were also constructed which contained null mutations in prkA and/or prkB. Studies utilizing these strains demonstrated that CO$\sb2$ fixation was critical for photoheterotrophic growth but could be replaced by the alternative reduction of dimethylsulfoxide. Thus, CO$\sb2$ fixation was identified as an essential mediator in maintaining cellular redox balance critical for photoheterotrophic growth. The product of phosphoribulokinase, ribulose 1,5-bisphosphate, is suggested to be one factor involved in the control of expression of ribulose 1,5-bisphosphate carboxylase/oxygenase. Each form of phosphoribulokinase and ribulose 1,5-bisphosphate carboxylase/oxygenase were shown to have distinct roles in CO$\sb2$ fixation, and the existence and location of a region encoding a repressor of prkA expression and an activator of rbcR expression (cfxR) was postulated.
|Rights Information:||Copyright 1989 Hallenbeck, Paul Leon|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9010872|