Predicted Glycosyl Transferase Genes Located Outside of the HEP Island are Required for Formation of Heterocyst Envelope Polysaccharide in Anabaena sp. strain PCC 7120

The State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei 430072, PR China, and MSU-DOE Plant Research Laboratory and Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824, U.S.A.

^* To whom correspondence should be addressed. Email: xux{at}ihb.ac.cn.

	Abstract

Heterocysts, during maturation, form an envelope layer of polysaccharide, denoted HEP, whose synthesis depends on a cluster of genes, the HEP island, and on an additional, distantly positioned gene, hepB or a gene immediately downstream from it. We show that HEP formation depends upon predicted glycosyl transferase genes all4160, at a third locus, and alr3699, adjacent to hepB and co-transcribed with it. Mutations in histidine kinase genes hepN and hepK appear to silence the promoter of hepB and incompletely down-regulate all4160.