生物
谷氨酰胺合成酶
生物化学
腺苷酸化
谷氨酰胺
操纵子
大肠杆菌
西格玛因子
氮同化
氨基酸
基因
分子生物学
RNA聚合酶
生物合成
作者
W.C. van Heeswijk,Sjouke Hoving,Douwe Molenaar,Brenda I. Stegeman,Daniel Kahn,Hans V. Westerhoff
标识
DOI:10.1046/j.1365-2958.1996.6281349.x
摘要
The PII protein has been considered pivotal to the dual cascade regulating ammonia assimilation through glutamine synthetase activity. Here we show that PII, encoded by the glnB gene, is not always essential; for instance upon ammonia deprivation of a glnB deletion strain, glutamine synthetase can be deadenylylated as effectively as in the wild-type strain. We describe a new operon, glnK amtB, which encodes a homologue of PII and a putative ammonia transporter. We cloned and overexpressed glnK and found that the expressed protein had almost the same molecular weight as PII, reacted with polyclonal PII antibody, and was 67% identical in terms of amino acid sequence with Escherichia coli PII. Like PII, purified GlnK can activate the adenylylation of glutamine synthetase in vitro, and, in vivo, the GlnK protein is uridylylated in a glnD-dependent fashion. Unlike PII, however, the expression of glnK depends on the presence of UTase, nitrogen regulator I (NRI), and absence of ammonia. Because of a NRI and a sigma N (sigma 54) RNA polymerase-binding consensus sequence upstream from the glnK gene, this suggests that glnK is regulated through the NRI/NRII two-component regulatory system. Indeed, in cells grown in the presence of ammonia, glutamine synthetase deadenylylation upon ammonia depletion depended on PII. Possible regulatory implications of this conditional redundancy of PII are discussed.
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