SPATIAL EXPRESSION AND AUTOREGULATION OF HETR, A GENE INVOLVED IN THECONTROL OF HETEROCYST DEVELOPMENT IN ANABAENA

The spatially patterned differentiation of heterocysts in the filament ous cyanobacterium Anabaena requires a functional hetR gene. Transcrip tional fusions to luxAB show that hetR is transcribed at a low level t hroughout the filament when Anabaena is grown with combined nitrogen, and that induction of the gene begins within 2 h following nitrogen de privation. By 3.5 h, induction is localized to spaced foci. By 6 h, th ere is an overall induction of at least threefold in whole cultures, r eflecting at least a 20-fold increase within spatially separated cells . The induction requires the presence of a functional hetR gene, indic ating that hetR is autoregulatory. Full induction of a heterocyst stru ctural gene, hepA also requires a functional hetR locus.