ALTERED PH AND LYSINE SIGNALING MUTANTS OF CADC, A GENE ENCODING A MEMBRANE-BOUND TRANSCRIPTIONAL ACTIVATOR OF THE ESCHERICHIA-COLI CADBA OPERON
ALTERED PH AND LYSINE SIGNALING MUTANTS OF CADC, A GENE ENCODING A MEMBRANE-BOUND TRANSCRIPTIONAL ACTIVATOR OF THE ESCHERICHIA-COLI CADBA OPERON
复制标题
DOI：
10.1111/j.1365-2958.1994.tb01262.x
复制
发表时间：
1994-10-01
影响因子：
3.6
通讯作者：
OLSON, ER
中科院分区：
文献类型：
--
作者：
DELL, CL;NEELY, MN;OLSON, ER
在低外部 pH 值和外源赖氨酸条件下，大肠杆菌 CadC 蛋白是 cadBA 转录激活所必需的。 cadBA 编码参与赖氨酸脱羧为尸胺以及尸胺排泄的蛋白质。序列分析表明，CadC 含有单个跨膜片段，将氨基末端的 DNA 结合结构域与周质结构域分开。亚细胞级分的 Western 分析表明，在诱导 pH (pH 5.8) 或非诱导 pH (pH 7.6) 下生长的细胞中，CadC 在细胞质膜中表达并浓缩。根据其独立于低外部 pH 值或外源赖氨酸表达 cadA-lacZ 融合体的能力，分离了八个 cadC 突变体。其中五个突变体在 pH 5.8 和 pH 7.6 下均表达 cadA-lacZ 融合体，但保留了对赖氨酸信号的要求，而其他三个突变体在赖氨酸存在下表现出 pH 独立性，在 pH 5.8 下表现出赖氨酸独立性，但在 pH 7.6 下则不然。这些结果支持这样一种模型，其中 CadC 是 cadBA 操纵子的膜结合转录激活剂，能够（直接或间接）感测由于酸性 pH 和赖氨酸而在细胞质膜外产生的信号。
The Escherichia coli CadC protein is required for activation of cadBA transcription under conditions of low external pH and exogenous lysine. cadBA encodes proteins involved in the decarboxylation of lysine to cadaverine, and cadaverine excretion. Sequence analysis suggested that CadC contains a single transmembrane segment separating a DNA-binding domain in the amino terminus from a periplasmic domain. Western analysis of subcellular fractions demonstrated that CadC is expressed and concentrated in the cytoplasmic membrane in cells grown either at an inducing pH (pH 5.8) or at a non-inducing pH (pH 7.6.). Eight cadC mutants were isolated based on their ability to confer expression of a cadA-lacZ fusion independent of low external pH or exogenous lysine. Five of these mutants expressed the cadA-lacZ fusion at both pH 5.8 and pH 7.6, but retained the requirement for the lysine signal while the other three mutants displayed pH independence in the presence of lysine, and lysine independence at pH 5.8 but not at pH 7.6. These results support a model in which CadC is a membrane-bound transcriptional activator of the cadBA operon capable of sensing (directly or indirectly) signals generated outside the cytoplasmic membrane as a consequence of acidic pH and lysine.