The hydC region contains a multi-cistronic operon (nik) involved in nickel transport in Escherichia coli.

We have cloned the multigenic hydC locus of Escherichia coli on a 7.1-kb BamHI-EcoRI fragment. Since its gene products are likely to be involved in the specific nickel transport [Wu et al., Mol. Microbiol. 3 (1989) 1709-1718], we propose a new gene designation, nik, to replace hydC. In vivo gene expression studies and complementation analysis support the notion that the nik locus is a multi-cistronic operon consisting of two to five genes. The first two genes, arranged in the order nikA and nikB, encode two proteins of 59 and 27.5 kDa, respectively. The downstream genes direct the biosynthesis of three polypeptides of 30, 28 and 25.5 kDa. Southern-blot analysis showed that mutant HYD720 carries a chromosomal deletion of 5.1-kb covering both nikA and nikB, whereas a 0.8-kb deletion in mutant HYD790 includes the sole nikB region. The cloned nik operon and the deletion mutants will aid greatly in the further molecular characterization of the multicomponent-specific transport of nickel in E. coli.