RNA structures involved in translational regulation of homing endonucleases in T-even bacteriophage. Arrows and red type indicate late promoter position and direction of transcription in the corresponding DNA sequence. For cases where the initating nucleotide has been mapped, it is indicated with a star. The RBS and start codon are shown in blue and black boldface type, respectively. Nucleotide variants in the I-TevI hairpin are indicated for phages TuIa and U5, and the alternative structure of the phage U5 I-TevIII hairpin is indicated by a box. The lower arrows indicate the general genetic organization of hairpin-regulated homing endonucleases. From left to right; the free-standing homing endonucleases mobE and segB, the intron-encoded endonucleases I-TevI, I-TevII, and I-TevIII, and the unusual hairpin for seg43(25) in Aeromonas phage 25.