CHARACTERIZATION OF HETR PROTEIN-TURNOVER IN ANABAENA SP. PCC-7120

The hetR gene plays an important role in heterocyst development and pa ttern formation in heterocystous cyanobacteria. The hetR gene from Ana baena sp. PCC 7120 was overexpressed in Escherichia coli. Antibodies r aised against the recombinant HetR protein (rHetR) were used to charac terize metabolism of the HetR of Anabaena sp. PCC 7120 in vivo. HetR w as present at a low level when Anabaena sp. PCC 7120 was grown in the presence of combined nitrogen. Shifting from nitrogen repletion condit ions to nitrogen depletion conditions led to a two fold increase of He tR in total cell extracts, and most of HetR was located in heterocysts . The amount of HetR in total cellular extracts increased rapidly afte r shifting to nitrogen depletion conditions and reached a maximum leve l 3 h after the shift. Isoelectrofocusing electrophoresis revealed tha t the native HetR had a more acidic isoelectric point than did rHetR. After combined nitrogen was added to the nitrogen-depleted cultures, t he degradation of HetR depended on culture conditions: before heterocy sts were fully developed, HetR was rapidly degraded; after heterocysts were fully developed, HetR was degraded much more slowly. The distrib ution of HetR in other species of cyanobacteria was also studied.