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Journal of Bacteriology, December 2001, p. 6841-6851, Vol. 183, No. 23
MSU-DOE Plant Research Laboratory, Michigan
State University, East Lansing, Michigan 48824
Received 6 June 2001/Accepted 12 September 2001
In many filamentous cyanobacteria, vegetative cells can
differentiate into heterocysts, cells that are specialized for aerobic fixation of N2. Synthesis of the heterocyst envelope
polysaccharide is dependent on the gene hepA in
Anabaena sp. strain PCC 7120. In search of genes that
are involved in the regulation of hepA, we transposon
mutagenized strain DR1069, which bears a chromosomal hepA::luxAB fusion. One
resulting mutant, designated HNL3, grows normally in medium with
nitrate and shows poor induction of hepA in response to
nitrogen deprivation. In HNL3, transposon Tn5-1058 is
inserted within gene hcwA, a constitutively expressed
open reading frame whose predicted product resembles
N-acetylmuramoyl-L-alanine amidases.
Reconstruction of the mutation confirmed that the mutant phenotype
resulted from the insertion of the transposon. The induction of
hepA in HNL3 is partially restored upon recombination of
HNL3 with plasmid-borne, wild-type hcwA. Moreover, HcwA
expressed in Escherichia coli exhibits wall-lytic
activity. These results suggest that the degradation, or possibly
reconstruction, of the cell peptidoglycan layer is a prerequisite for
heterocyst maturation.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.23.6841-6851.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
HcwA, an Autolysin, Is Required for Heterocyst
Maturation in Anabaena sp. Strain PCC 7120


and
*
Corresponding author. Mailing address: MSU-DOE Plant
Research Laboratory, Michigan State University, East Lansing, MI 48824. Phone: (517) 353-2049. Fax: (517) 353-9168. E-mail:
wolk{at}msu.edu.
Present address: Department of Entomology, Michigan State
University, East Lansing, MI 48824.
Present address: Schering-Plough Research Institute, Kenilworth,
NJ 07033-0539.
§
Present address: Department of Crop and Soil Sciences, Michigan
State University, East Lansing, MI 48824.
Permanent address: N. Vavilov Institute of General Genetics,
Moscow 117809, Russia.
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