Fig. 3.

Occurrence of a palindrome, 5′ TCCGGA, in promoters of the DIF⁺ category. (A) Alignment of the heterocyst-specific promoters for NsiR1, the hetR TSS3, sigC, and hetC with selected promoters in the DIF⁺ category (fold change ≥ 8) containing TCCGGA around position −35 (one mismatch allowed). (B) Cell-specific transcription from the wild-type promoter of NsiR1 (P6; Upper) or a mutated version of P6 carrying GAATTC instead of TCCGGA (Lower). Images corresponding to red autofluorescence (Right) and GFP fluorescence (Left) are shown. White triangles point to proheterocysts. (Scale bars: 10 μm.)