(A) β-Galactosidase activity 18 h after induction of heterocyst differentiation for the wild type bearing the −271 tsp-lacZ fusion in plasmid pRR143, the patA mutant UHM101 bearing the −271 tsp-lacZ fusion in plasmid pRR143, the wild type bearing the −728/−696(+132) tsp-lacZ fusion in plasmid pRR152, the wild type bearing the −728/−696(+132) tsp-lacZ fusion in plasmid pRR152 with 6 μM PatS-5 included in the medium, the wild type bearing the control plasmid pNC101, and the patA mutant UHM101 bearing control plasmid pNC101. WT, wild type; S-5, PatS-5; ONP, o-nitrophenol. (B) Transcription from the −271 tsp at different times after induction of heterocyst differentiation. Diamonds, β-galactosidase activity of the wild type bearing the −271 tsp-lacZ fusion; squares, β-galactosidase activity of the wild type bearing control plasmid pNC101.