FIG. 1.

Genetic organization of the par locus. The par locus is approximately 400 bp in size, delimited by the promoters for the RNA I and RNA II genes located on the right and left ends, respectively, and is shown by a heavy black line. The relative lengths of the RNA I and RNA II transcripts are depicted as arrowed lines below and above the genetic map, respectively. The fst toxin-encoding gene is depicted on the RNA I gene and transcript with a hatched box. The direct repeats DRa and DRb and the inverted repeat of the bidirectional rho-independent transcription terminator are shown by white arrows. These sequences provide the complementary regions required for interaction of RNA I and RNA II, since transcription occurs in opposite directions across the repeats. Note also that the DRa and DRb sequences overlap the translation initiation region of fst in RNA I. The sequence of the toxic Fst peptide is shown below the map.