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Category: Bacterial Pathogenesis; Microbial Genetics and Molecular Biology
Biosynthesis of Glutamine and Glutamate and the Assimilation of Ammonia, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555818388/9781555810535_Chap20-1.gif /docserver/preview/fulltext/10.1128/9781555818388/9781555810535_Chap20-2.gifAbstract:
Regulation of the enzymes involved in glutamine and glutamate biosynthesis in Bacillus spp and their roles in ammonia assimilation is the focus of this chapter. For most bacteria, assimilation of ammonia is accomplished through the synthesis of glutamine and glutamate. Alanine dehydrogenase and asparagine synthetase have also been implicated in assimilation, and their roles are discussed. The Bacillus spp can be separated into three groups based on the pathway used for assimilation. One group, represented by B. subtilis, employs glutamine synthetase (GS) and GOGAT for assimilation. The second, which contains most members of the genus, utilizes all three enzymes, depending on nutritional environment. The third group uses only GDH for assimilation, a characteristic of some N2-fixing Bacillus spp. Assimilation of ammonia in derivatives of B. subtilis 168 and SMY is solely accomplished through the coupled action of GS and GOGAT. A catabolic role for GDH is consistent with the notion that GOGAT is solely responsible for glutamate biosynthesis in B. subtilis. The production of glutamate from glutamine is accomplished by the enzyme L-glutamine aminohydrolase, also known as glutaminase.
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glnRA operon in B. subtilis. (a) Structure of the operon and model for control. Autogenous control of glnRA expression from the glnRA promoter, glnRAp, involves glnR and glnA gene products GlnR and GS, respectively. GlnR represses transcription under excess-nitrogen conditions by binding to glnRA operators glnRAOi and glnRAo 2 , thereby inhibiting transcription initiation. GlnR activity is thought to be mediated in part by GS, which may be used to relay information about the nitrogen state of the cell, (b) Sequence of the glnRA promoter region from -71 to +5 relative to the start point of transcription ( 116 ). Boxed sequences indicate -10 and -35 promoter regions. Diverging arrows indicate symmetrical glnRAo l (-40 to -60) and quasisymmetrical glnRAo 2 (-17 to -37) sites shown to be involved in GlnR binding.
glnRA operon in B. subtilis. (a) Structure of the operon and model for control. Autogenous control of glnRA expression from the glnRA promoter, glnRAp, involves glnR and glnA gene products GlnR and GS, respectively. GlnR represses transcription under excess-nitrogen conditions by binding to glnRA operators glnRAOi and glnRAo 2 , thereby inhibiting transcription initiation. GlnR activity is thought to be mediated in part by GS, which may be used to relay information about the nitrogen state of the cell, (b) Sequence of the glnRA promoter region from -71 to +5 relative to the start point of transcription ( 116 ). Boxed sequences indicate -10 and -35 promoter regions. Diverging arrows indicate symmetrical glnRAo l (-40 to -60) and quasisymmetrical glnRAo 2 (-17 to -37) sites shown to be involved in GlnR binding.
glnA gene of C. acetobutylicum. The schematic diagram shows orientation of the glnA transcript as directed from either of two promoters, pi and p2, and a putative anti-g/иА transcript expressed from promoter p3 from the opposite strand. Boxes at the beginning of each message represent regions whose sequences, shown relative to the start point of the glnA open reading frame, are complementary to each other (see text).
glnA gene of C. acetobutylicum. The schematic diagram shows orientation of the glnA transcript as directed from either of two promoters, pi and p2, and a putative anti-g/иА transcript expressed from promoter p3 from the opposite strand. Boxes at the beginning of each message represent regions whose sequences, shown relative to the start point of the glnA open reading frame, are complementary to each other (see text).
gltAB and gltC genes of B. subtilis. Synthesis of GOGAT large and small subunits, coded for by gltA and gltB, respectively, are shown to occur from a monocistronic message, although such has not been established. The GltC protein, produced by gltC, represses its own synthesis and is also required for activation of transcription from the gltAp promoter under glutamate-limited growth conditions. The overlap of the two promoters and the presence of several repeated sequences within the gltAp and gltCp regions are thought to play roles in regulating gitA(B) transcription (see text).
gltAB and gltC genes of B. subtilis. Synthesis of GOGAT large and small subunits, coded for by gltA and gltB, respectively, are shown to occur from a monocistronic message, although such has not been established. The GltC protein, produced by gltC, represses its own synthesis and is also required for activation of transcription from the gltAp promoter under glutamate-limited growth conditions. The overlap of the two promoters and the presence of several repeated sequences within the gltAp and gltCp regions are thought to play roles in regulating gitA(B) transcription (see text).
GOGAT and GDH in gram-positive bacteria
GOGAT and GDH in gram-positive bacteria