FIG. 2.

Genome arrangement and transcription patterns surrounding the stx genes of the Stx-encoding phages (A) and gene structures of mutant strains (B). This diagram is based on the characterized Stx-encoding phages (44, 45). Shown are relevant genes, promoters, terminators, and transcripts for the expression and distribution of Shiga toxins. Following prophage induction, repressor cleavage allows for increased early transcription and then the production of antitermination Q protein. It facilitates transcription initiating at the late promoter by readthrough at the terminator located downstream of the Q gene. On the other hand, transcription initiating at the Stx1 promoter is inducible in low-iron conditions.