I. Induction of mbgA、melB gene expression by galactose and poly-β- hydroxybutyrate metabolism in Bacillus megateriumII. Characterization of the FabG4 protein of Mycobacterium tuberculosis

• Main Authors: Wei-Ting Lin, 林蔚婷
• Other Authors: Gwo-Chyuan Shaw
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/35063778410228727078

碩士 === 國立陽明大學 === 生化暨分子生物研究所 === 95 === It has been established that expression of Bacillus megaterium mbgA and melB genes, which encode a β- and an α-galactosidase, respectively, can be induced by lactose and repressed by glucose. In this study we demonstrated that galactose could induce expression of mbgA and melB genes to a greater extent than lactose. The bgaR gene, which is located immediately upstream of the mbgA gene and encodes a transcriptional activator, has been demonstrated to be involved in galactose induction of β-galactosidase activities. In contrast, galactose induction of α-galactosidase activities is not BgaR-dependent. Two–dimentional proteomic analysis and mass- spectrometry analysis showed that galactose could increase HPr protein level. However, the mechanism for galactose induction of the HPr protein remains to be further investigated. PHAs (Polyhydroxyalkanoates) are polyesters that were synthesized and accumulated as granules in bacteria. PHB (poly-β-hydroxybutyrate) is the most common form of PHAs. Previous studies have shown that PHB accumulation in B. megaterium was inhibited when glucose was added to LB medium. In this study, PHB content analysis showed that higher concentrations of glucose could repress PHB accumulation in B. megaterium grown in M9 minimal medium. We have also found that there is no difference in the rate of PHB breakdown in the presence of a high or low concentration of nitrogen source. In an attempt to identify possible regulators that might control the PHB accumulation in B. megaterium, we found that disruption of the spo0A gene could considerably reduce PHB accumulation. Its mechanism remains to be clarified. FabG4, a possible β-ketoacyl-ACP reductase of Mycobacterium tuberculosis, is longer than other FabG proteins by 200 amino acid residues at N-terminal side. We examined its enzymatic activity and possible interaction with FadA2, a putative β-ketoacyl coenzyme A cleavage enzyme encoded by the adjacent gene fadA2. It was found that neither full-length nor N-terminally truncated FabG4 has β-ketoacyl-ACP reductase activity. In addition, bacterial two-hybrid analysis showed that no interaction exists between FabG4 and FadA2. The physiological role of FabG4 in M. tuberculosis remains to be investigated.