Journal of Bacteriology, August 1998, p. 4233-4242, Vol. 180, No. 16
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

andMSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824
Received 27 March 1998/Accepted 4 June 1998
In Anabaena spp., synthesis of the heterocyst envelope
polysaccharide, required if the cell is to fix dinitrogen under aerobic conditions, is dependent on the gene hepA. A
transcriptional start site of hepA was localized 104 bp 5'
from its translational initiation codon. A 765-bp open reading frame,
denoted hepC, was found farther upstream. Inactivation of
hepC led to constitutive expression of hepA and
prevented the synthesis of heterocyst envelope polysaccharide. However,
the glycolipid layer of the heterocyst envelope was synthesized. A
hepK mutation blocked both the synthesis of the heterocyst
envelope polysaccharide and induction of hepA. The
predicted product of hepK resembles a sensory
protein-histidine kinase of a two-component regulatory system. Analysis
of the region between hepC and hepA indicated
that DNA sequences required for the induction of hepA upon
nitrogen deprivation are present between bp
574 and
440 and between
bp
340 and
169 relative to the transcriptional start site of
hepA. Gel mobility shift assays provided evidence that one
or more proteins bind specifically to the latter sequence. The Fox box
sequence downstream from hepA appeared inessential for the
induction of hepA.
Present address: Department of Entomology, Michigan State
University, East Lansing, MI 48824.
Present address: Department of Microbiology, Michigan State
University, East Lansing, MI 48824.
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