The NtcA-activated amt1 gene encodes a permease required for uptake of low concentrations of ammonium in the cyanobacterium Synechococcus sp. PCC 7942 The GenBank accession number for the nucleotide sequence of the amt1 gene described in this paper is AJ311900.

Abstract

In the unicellular cyanobacterium Synechococcus sp. PCC 7942, ammonium/methylammonium transport activity has been characterized but ammonium transport genes have not been described. The amt1 gene encoding a permease responsible for high-affinity [ 14 C]methylammonium transport in Synechococcus sp. PCC 7942 was cloned and inactivated. The Amt1 permease appeared essential to take up ammonium when it was present at low concentrations in the external medium and might also be involved in recapture of ammonium leaked out from the cells. Expression of amt1, which was induced in the absence of ammonium and also influenced by the inorganic carbon supply, was dependent on the NtcA transcriptional regulator. The promoter of amt1 was found to exhibit the structure of NtcA-activated promoters, and specific binding of purified NtcA to amt1 promoter sequences was observed. The results of this study indicate that amt1 belongs to the NtcA regulon and that NtcA may respond to both nitrogen and carbon availability.

PipX, the coactivator of NtcA, is a global regulator in cyanobacteria

“…In addition to this orthodox promoter structure, which matches that of the Escherichia coli class II Crp-dependent promoters, NtcA can activate from positions further upstream or from sequences not matching the reported consensus (21). NtcA binding motifs were found in a few genes or operons experimentally characterized in S. elongatus (22)(23)(24) and in others predicted to be controlled by NtcA in the cyanobacterium S. elongatus PCC 6301 (25), which is almost identical to S. elongatus. Remarkably, NtcA binding motifs were found in association with 29 of the 30 transcription units in class 4 ( Fig.…”

Acclimation of unicellular cyanobacteria to macronutrient deficiency: emergence of a complex network of cellular responses

“…Activated NtcA enhances transcription of ntcA and glnB as well as other classical NtcA promoters, and may switch from an inactive state (NtcA i ) to an activated state (NtcA a ). NtcA-dependent genes of the ammonium assimilation pathway include amt1, glnA and nir (Vazquez-Bermudez et al, 2002a). Furthermore, NtcA stimulates expression of the alternative sigma factor gene rpoD, and of the alternative glutamine synthetase gene glnN, exhibiting a non-canonical NtcA-binding promoter sequence.…”

The NtcA-Dependent P 1 Promoter Is Utilized for glnA Expression in N 2 -Fixing Heterocysts of Anabaena sp. Strain PCC 7120

“…NtcA belongs to the CAP family of bacterial transcriptional regulators, and the promoter structure just described is similar to that of the class II CAP-dependent promoters (7). NtcA functions in response to the C/N balance of the cell, and 2-oxoglutarate has been identified as a putative effector of NtcA (35,44,(46)(47)(48). The ntcA gene appears to be autoregulatory, and ntcA expression, which takes place at a basal level in the presence of ammonium, increases in response to nitrogen limitation (21,22,34,38,49).…”