Figure 1.

The tryptophan-recapture operon of Chlamydophila psittaci (Cps). Genes are color-coded as shown in the key. Arrows indicate the direction of transcription. The nomenclature for tryptophan-pathway genes is that elaborated by Xie et al. [30], whereby genes encoding the five enzymes are named in order of the pathway steps. The two subunits of the first and fifth steps are given additional lower-case identifiers, that is, trpAa/trpAb and trpEa and trpEb (for simplicity, the trp genes are labeled without the trp identifier). Nucleotide spacing between genes is shown; negative values indicate open reading frames that overlap (translational coupling). The membrane-attack complex/perforin family protein from the chlamydiae, which belongs to PFAM protein family HMM PFO1823, has been discussed by Ponting [59]. The gene encoding this protein in C. psittaci appears to have multiple frameshifts, a possible carboxy-terminal truncation, and a possible insertion. Whether sequencing errors might account for this is unknown at the present time. Cpn, Chlamydophila pneumoniae.