FIG 5.

Proposed relationship between environmental cues and TT formation. Based on our data and what has been shown previously for the regulation of TT in S. Typhi, at neutral pH, transcription of pltB is induced by PhoP (30), which may lead to the preferential inclusion of PltB in the TT binding subunit. Conversely, at slightly acidic pH, SsrB induces transcription of artB (32) in a pH-sensitive manner (47), which may favor preferential inclusion of ArtB in the TT binding subunit. The copurification of ArtB and PltB suggests the potential formation of heteropentameric forms of the binding subunit, although a role for these heteropentameric subunits will require further investigation.