Affiliation:
1. H. Steinitz Marine Biology Laboratory, Interuniversity Institute for Marine Sciences, Eilat 88103,1 and
2. Department of Microbial and Molecular Ecology, Hebrew University of Jerusalem, Jerusalem,2 Israel
Abstract
ABSTRACT
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.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
88 articles.
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