FIG. 1.

The ppk ppx operon in V. cholerae and recombinant plasmids. (A) The large box represents the cloned and sequenced 4-kb NcoI-PstI chromosomal fragment containing the operon. ORFs are indicated by arrows. The lines under the box indicate the portions of the ppk ppx region inserted in the plasmids indicated to the left. The nonunique EcoRI and EcoRV restriction sites in the 4-kb NcoI-PstI fragment are denoted by subscripts. (B) Putative pho box sequence in the ppk promoter region. (C) Sequence overlap between the ppk and ppx ORFs. The center sequence is the nucleotide sequence of the ppk ppx ORF junction, and the top and bottom sequences are the deduced amino acid sequences for PPK and PPX, respectively. (D) Putative transcriptional terminator sequence in the region downstream of ppx. The pair of sequences indicated by the arrows have the potential to form a stem-loop structure. The underlined nucleotides are the indicated start and stop codons.