Mutations in four regulatory genes have interrelated effects on heterocyst maturation in Anabaena sp. strain PCC 7120

J Bacteriol. 2006 Nov;188(21):7387-95. doi: 10.1128/JB.00974-06. Epub 2006 Aug 25.


Regulatory genes hepK, hepN, henR, and hepS are required for heterocyst maturation in Anabaena sp. strain PCC 7120. They presumptively encode two histidine kinases, a response regulator, and a serine/threonine kinase, respectively. To identify relationships between those genes, we compared global patterns of gene expression, at 14 h after nitrogen step-down, in corresponding mutants and in the wild-type strain. Heterocyst envelopes of mutants affected in any of those genes lack a homogeneous, polysaccharide layer. Those of a henR mutant also lack a glycolipid layer. patA, which encodes a positive effector of heterocyst differentiation, was up-regulated in all mutants except the hepK mutant, suggesting that patA expression may be inhibited by products related to heterocyst development. hepS and hepK were up-regulated if mutated and so appear to be negatively autoregulated. HepS and HenR regulated a common set of genes and so appear to belong to one regulatory system. Some nontranscriptional mechanism may account for the observation that henR mutants lack, and hepS mutants possess, a glycolipid layer, even though both mutations down-regulated genes involved in formation of the glycolipid layer. HepK and HepN also affected transcription of a common set of genes and therefore appear to share a regulatory pathway. However, the transcript abundance of other genes differed very significantly from expression in the wild-type strain in either the hepK or hepN mutant while differing very little from wild-type expression in the other of those two mutants. Therefore, hepK and hepN appear to participate also in separate pathways.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Anabaena / chemistry
  • Anabaena / genetics*
  • Anabaena / growth & development
  • Bacterial Proteins / genetics
  • Bacterial Proteins / physiology
  • Gene Deletion
  • Gene Expression Profiling
  • Gene Expression Regulation, Bacterial*
  • Genes, Bacterial
  • Genes, Regulator*
  • Glycolipids / analysis
  • Oligonucleotide Array Sequence Analysis
  • Polysaccharides, Bacterial / analysis
  • RNA, Bacterial / analysis
  • RNA, Messenger / analysis
  • Regulon / genetics
  • Transcription, Genetic


  • Bacterial Proteins
  • Glycolipids
  • HepK protein, Anabaena
  • Polysaccharides, Bacterial
  • RNA, Bacterial
  • RNA, Messenger