Regulation of ntcA expression and nitrite uptake in the marine Synechococcus sp. strain WH 7803
Regulation of ntcA expression and nitrite uptake in the marine Synechococcus sp. strain WH 7803
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DOI：
10.1128/jb.180.7.1878-1886.1998
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发表时间：
1998-04-01
影响因子：
3.2
通讯作者：
Post, AF
中科院分区：
文献类型：
--
作者：
Lindell, D;Padan, E;Post, AF
NtcA是一种转录激活因子，参与蓝藻的氮素调控。在缺乏铵的情况下，它调节一系列编码蛋白质的基因的转录，这些蛋白质是吸收和同化替代氮源所需的（I. Luque，E.弗洛雷斯和A. Herrero，EMBO J. 13：2862-2869，1994）。ntcA以单拷贝存在于海洋聚球藻属菌株WH 7803中，已被克隆并测序。推定的氨基酸序列显示出高度的同一性，从淡水蓝藻的NtcA在两个功能域。从一个假定的转录起始点位于下游的NtcA共识识别序列的铵负调控的表达。添加利福平或铵导致ntcA转录水平快速下降，在两种情况下半衰期均小于2分钟。硝酸盐生长的细胞表现出高的ntcA转录水平，以及活性亚硝酸盐吸收的能力。然而，铵生长的细胞表现出低水平的ntcA转录，并没有利用亚硝酸盐。亚硝酸盐摄取活性细胞的铵的加入导致在24小时内的摄取率逐渐下降。在转移到缺乏氮源的培养基中的细胞中未诱导活性亚硝酸盐摄取，尽管有证据表明ntcA表达升高，表明ntcA表达不足以使摄取能力发展。硝酸盐和亚硝酸盐的添加导致亚硝酸盐吸收的发展，而亮氨酸的添加没有。此外，亚硝酸盐添加引发从头蛋白质合成所需的吸收能力的发展。这些数据表明，亚硝酸盐和硝酸盐作为特定的诱导剂的亚硝酸盐吸收所需的蛋白质的合成。
NtcA is a transcriptional activator involved in global nitrogen control in cyanobacteria. In the absence of ammonium it regulates the transcription of a series of genes encoding proteins required for the uptake and assimilation of alternative nitrogen sources (I. Luque, E. Flores, and A. Herrero, EMBO J. 13:2862-2869, 1994). ntcA, present in a single copy in the marine Synechococcus sp. strain WH 7803, was cloned and sequenced. The putative amino acid sequence shows a high degree of identity to NtcA from freshwater cyanobacteria in two functional domains. The expression of ntcA was negatively regulated by ammonium from a putative transcription start point located downstream of an NtcA consensus recognition sequence. Addition of either rifampin or ammonium led to a rapid decline in ntcA transcript levels with half-lives of less than 2 min in both cases. Nitrate-grown cells showed high ntcA transcript levels, as well as the capacity for active nitrite uptake. However, ammonium-grown cells showed low levels of the ntcA transcript and did not utilize nitrite. The addition of ammonium to nitrite uptake-active cells resulted in a gradual decline in the rate of uptake over a 24-h period. Active nitrite uptake was not induced in cells transferred to medium lacking a nitrogen source despite evidence of elevated expression of ntcA, indicating that ntcA expression is not sufficient for uptake capacity to develop. Nitrate and nitrite addition led to the development of nitrite uptake, whereas the addition of leucine did not. Furthermore, nitrite addition triggered the de novo protein synthesis required for uptake capacity to develop. These data suggest that nitrite and nitrate act as specific inducers for the synthesis of proteins required for nitrite uptake.