Fig. 3.

Extracopy hetN fails to suppress heterocyst differentiation in a strain carrying the hetRR223W allele. Wild-type Anabaena PCC 7120 (A) and the reconstructed merodiploid AMC1287 (B) strains bearing plasmid pAM1537, which carries hetN under the control of the copper-inducible petE promoter, 2 days after transfer to combined nitrogen-free BG-11₀ plates. The copper concentration in standard BG-11 and BG-11₀ medium should produce approximately half-maximal expression from the petE promoter (8).