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J Bacteriol, April 1998, p. 1878-1886, Vol. 180, No. 7
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Regulation of ntcA Expression and
Nitrite Uptake in the Marine Synechococcus sp. Strain
WH 7803
Debbie
Lindell,1,2
Etana
Padan,2 and
Anton F.
Post1,2,*
H. Steinitz Marine Biology Laboratory,
Interuniversity Institute for Marine Sciences, Eilat
88103,1 and
Department of Microbial
and Molecular Ecology, Hebrew University of Jerusalem,
Jerusalem,2 Israel
Received 11 September 1997/Accepted 20 January 1998
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.
*
Corresponding author. Mailing address: Interuniversity
Institute for Marine Sciences, H. Steinitz Marine Biology Laboratory, P.O. Box 469, Eilat 88103, Israel. Phone: 972-76-360-122. Fax: 972-76-374-329. E-mail: anton{at}vms.huji.ac.il.
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