Summary:

1. TroA has significant sequence similarity to a family of Gram-negative periplasmic substrate-binding proteins and to a family of streptococcal proteins that may have dual roles as substrate binding proteins and adhesins. TroB is homologous to the ATP-binding protein component, whereas TroC and TroD are related to the hydrophobic membrane protein components of ABC transport systems. TroR is similar to Gram-positive iron-activated repressor proteins (DesR, DtxR, IdeR, and SirR). The last open reading frame (ORF) of the tro operon encodes a protein that is highly homologous to the glycolytic pathway enzyme, Phosphoglycerate mutase (Pgm). Primer extension results demonstrated that the tro operon is transcribed from a sigma 70-type promoter element. Northern analysis and reverse transcriptase-polymerase chain reactions provided evidence for the presence of a primary 1-kb troA transcript and a secondary, less abundant, troA-pgm transcript. The presence of a complex operon containing a putative ABC transport system and a DtxR homolog indicates a possible linkage between transport and gene regulation in TP. (Gene 1997 Sep 15;197(1-2):47-64 PMID: 9332349, UI: 97473495 ).

2. ZnuABC are involved in the high-affinity zinc uptake transport system. Zur(b4046) acts as a negative controlling element binding to the bidirectional promoter region of znuA and znuBC, employing Zn(2+) as a cofactor to bind the operator of the repressed genes (ZnuACB) (Mol Microbiol 1998 Jun;28(6):1199-210 The ZnuABC high-affinity zinc uptake system and its regulator Zur in Escherichia coli. Patzer SI, Hantke K PMID: 9680209, UI: 98343803).

3. The ycdH operon encodes a high-affinity zinc transporter. Zur is a metalloregulatory protein related to the ferric uptake repressor (Fur) family of regulators and is required for the zinc-specific repression of two operons implicated in zinc uptake, yciC and ycdHIyceA (J Bacteriol 1998 Nov;180(22):5815-21 PMID: 9811636, UI:99030300).

4. CT069 is the fusion protein which has the C-terminal troR domain.