The gene for a novel cation/H+ antiporter from Puccinellia tenuiflora, PutCAX1, was cloned from a cDNA library. The PutCAX protein was localized in the vacuolar membrane using a GFP marker. Several yeast transformants were created using full-length and truncated form of PutCAX1 and their growths in the presence of various cations (Mg2+, Ca2+, Mn2+, Ni2+, Cu2+, Zn2+, Se2+, and Ba2+) were analyzed. PutCAX1 expression was found to affect the response to Ca2+ and Ba2+ in yeast. The PutCAX1 and C-terminally truncated PutCAX1 (Delta CPutCAX1) transformants grew in the presence of 70 mM Ca2+ as well as in the presence of 8 mM Ba2+. However, the Delta CPutCAX1 transformant was able to grow in the presence of 20 mM Ba2+ while the PutCAX1 transformant could not. On the other hand, expression of the N-terminally truncated form and the N- and C-terminally truncated form failed to suppress the Ca2+ or Ba2+ sensitivity of yeast. These results Suggest that PutCAX1 can complement the active Ca2+ transporters at some level and confer yeast Ba2+ tolerance, and that the N- and C-terminal regions of PutCAX1 play important roles in increasing the Ca2+ or Ba2+ tolerance of yeast. (C) 2009 Elsevier Inc. All rights reserved.