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The ''gab'' operon is responsible for the conversion of γ-aminobutyrate (GABA) to succinate. The ''gab'' operon comprises three structural genes – ''gabD'', ''gabT'' and ''gabP'' – that encode for a succinate semialdehyde dehydrogenase, GABA transaminase and a GABA permease respectively. There is a regulatory gene ''csiR'', downstream of the operon, that codes for a putative transcriptional repressor and is activated when nitrogen is limiting. The ''gab'' operon has been characterized in ''Escherichia coli'' and significant homologies for the enzymes have been found in organisms such as ''Saccharomyces cerevisiae'', rats and humans. Limited nitrogen conditions activate the ''gab'' genes. The enzymes produced by these genes convert GABA to succinate, which then enters the TCA cycle, to be used as a source of energy. The ''gab'' operon is also known to contribute to polyamine homeostasis during nitrogen-limited growth and to maintain high internal glutamate concentrations under stress conditions. == Structure == The ''gab'' operon consists of three structural genes: * ''gabT'' : encodes a GABA transaminase that produces succinic semialdehyde. * ''gabD'' : encodes an NADP-dependent succinic semialdehyde dehydrogenase, which oxidizes succinic semialdehyde to succinate. * ''gabP'' : encodes a GABA-specific permease. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gab operon」の詳細全文を読む スポンサード リンク
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