Heterodimeric inorganic cation antiporter, UmpAB, both subunits belonging to the DUF1538 family.  Genomic DNA was screened for novel Na⁺/H⁺ antiporter genes from Halomonas zhaodongensis by selection in Escherichia coli KNabc lacking three major Na⁺/H⁺ antiporters (Meng et al. 2017). Co-expression of two genes designated umpAB, encoding paired homologous unknown membrane proteins belonging to DUF1538 family, were found to confer E. coli KNabc tolerance to 0.4 M NaCl and 30 mM LiCl, and an alkaline pH resistance at 8.0. UmpAB localizes as a hetero-dimer in the cytoplasmic membrane and exhibits pH-dependent Na⁺(Li⁺, K⁺)/H⁺ antiport activity at a wide pH range of 6.5 to 9.5 with an optimal pH at 9.0. Neither UmpA nor UmpB showed homology with known single-gene or multi-gene Na⁺/H⁺ antiporters, and thus, UmpAB represents a novel two-component Na⁺(Li⁺, K⁺)/H⁺ antiporter (Meng et al. 2017).