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Expression of furA is modulated by NtcA and strongly enhanced in heterocysts of Anabaena sp. PCC 7120

S. López-Gomollón^1,2,

J. A. Hernández^1,,

¹ Department of Biochemistry and Molecular and Cell Biology, University of Zaragoza, Zaragoza, Spain
² Biocomputation and Complex Systems Physics Institute (BiFi), University of Zaragoza, Zaragoza, Spain
³ MSU-DOE Plant Research Laboratory and Department of Plant Biology, Michigan State University, East Lansing, MI, USA

Correspondence
M. F. Fillat
fillat{at}unizar.es

Fur (ferric uptake regulator) proteins are principally responsible for maintaining iron homeostasis in prokaryotes. Iron is usually a scarce resource. Its limitation reduces photosynthetic rates and cell growth in cyanobacteria in general and especially in cyanobacteria that are fixing dinitrogen, a process that requires the synthesis of numerous proteins with a high content of iron. This paper shows that in the diazotrophic cyanobacterium Anabaena sp. strain PCC 7120, levels of furA mRNA and FurA protein increase significantly in response to nitrogen deprivation, and that furA up-regulation takes place specifically in proheterocysts and mature heterocysts. Great differences in a Northern blot, probed with furA, of RNA from an ntcA mutant relative to wild-type Anabaena sp. were attributable to binding of NtcA, a global regulator of nitrogen metabolism, to the promoter of furA and to the promoter of the furA antisense transcript alr1690--furA.

A supplementary figure showing the construction of plasmids is available with the online version of this paper.

These authors contributed equally to this work.

Present address: Plant and Microbial Biology Department, 211 Koshland Hall, University of California at Berkeley, 94720 Berkeley, CA, USA.