9.B.10 The Putative Tripartite Zn2 Transporter (TZT) Family
Gaballa et al., 2002 have suggested that the yciABC genes, in Bacillus subtilis, in a single operon, encode a zinc transporter. These genes are regulated by the zinc uptake repressor, Zur. Analysis of a yciA-lacZ fusion indicated that this operon is induced under zinc starvation conditions and derepressed in the zur mutant. Phenotypic analyses suggest that the YciA, YciB, and YciC proteins may function as part of the same Zn(II) transport pathway. Mutation of yciA or yciC, singly or in combination, had little effect on growth of the wild-type strain but significantly impaired the growth of the ycdH mutant under conditions of zinc limitation. Since the YciA, YciB, and YciC proteins are not obviously related to any known transporter family, they may define a new class of metal ion uptake systems. Mutant strains lacking all three identified zinc uptake systems (YciABC, YcdHI-YceA, and ZosA) are dependent on micromolar levels of added zinc for optimal growth.
The three proteins, YciA, B and C are annotaed as a GTP cyclohydrolase (FolE2), a transpeptidase (DUF5011), and a metal chaparone protein, respectively. It is quite likely that these proteins do not function in transport in spite of the suggestion of Gaballa et al. (2002).