A study of the catabolite repression of the dehalogenase IVa gene of Burkholderia cepacia MBA4

by Yuen, Hiu-fung

Abstract (Summary)
(Uncorrected OCR) Abstract of the thesis entitled A STUDY OF THE CATABOLITE REPRESSION OF THE DEHALOGENASE IVa GENE OF Burkholderia cepacia MBA4 Submitted by Yuen Hiu Fung for the degree of Master of Philosophy at The University of Hong Kong in August 2004 Deh4a is encoded in a haloacids operon and expression of Deh4a is induced by 2-haloacids such as monochoroacetate (MCA). Carbon Catabolite repression control (CRC) has been reported in the degradation of many carbon sources but has not been previously investigated in the degradation of 2-haloacids. In this study, the haloacids operon was demonstrated to be under CRC. Transcription of the haloacids operon was repressed by nutrient-rich medium and succinate to 0.79% and 15% of the MCA induced level, respectively. Western analysis confirmed a reduced protein level under these conditions. Tn5 transposon mutagenesis was used to isolate mutants with relieved CRC. One transconjugant, 131M04, was found to possess ~3-fold relieved repression of the haloacids operon in rich medium. The DNA sequence of the corresponding wild-type gene was determined to encode a putative branched-chain amino acid (BCA) transporter (BAT). Cloning and expression of this ORF in an E. coli strain defective in BCA transport rescued the capability of the cells to transport isoleucine. When MBA4 was cultivated in minimal medium with MCA and BCA, expression of the haloacids operon is repressed to 46% of the level when BCA was absent. This repression effect was relieved in strain 131M04. These results indicate that expression of the haloacids operon is repressed by the presence of BCA and mutation of the BAT partially relieved the CRC conferred by rich medium and BCA.
Bibliographical Information:


School:The University of Hong Kong

School Location:China - Hong Kong SAR

Source Type:Master's Thesis

Keywords:pseudomonas genetics operons haloacid dehalogenase genetic regulation


Date of Publication:01/01/2005

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