J. Biochem, 2004, Vol. 135, No. 1 139-148
© 2004 The Japanese Biochemical Society
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A Conserved Domain in the Tail Region of the Saccharomyces cerevisiae Na+/H+ Antiporter (Nha1p) Plays Important Roles in Localization and Salinity-Resistant Cell-Growth
Department of Biological Sciences, Graduate School of Science, Osaka University, 1-16 Machikaneyama-cho, Toyonaka City, Osaka 560-0043
The Saccharomyces cerevisiae Na+/H+ antiporter Nha1p has a two-domain structure consisting of an N-terminal integral membrane region and a C-terminal cytoplasmic region. We previously identified six distinct cytoplasmic domains (C1C6) conserved among yeast species and here we performed detailed structure-function analysis of the C1 domain (16 residues). Deletion of the C1 domain causes extensive inhibition of cell-growth under high salinity conditions. Mutants with single residue deletions or various amino acid substitutions affecting the C1 domain were analyzed with respect to salinity-dependent growth and Nha1p localization. The C1 domain was found to consist of two subdomains: (i) The first three N-proximal residues, which in conjunction with the integral membrane region play a crucial role in the targeting of Nha1p to the cytoplasmic membrane, and (ii) the portion between Leu-439 and Thr-449, which is not required for localization, but in which four residues (Gly-440, Arg-441, His-442, and Ile-446) affect salinity-sensitive cell-growth by possibly influencing the antiporter activity. Based on the overall similarity of the two-domain structure of Nha1p to that of mammalian Na+/H+ antiporters, the functional importance of domains proximal to the membrane region is discussed.
* To whom correspondence should be addressed. E-mail: kanazawa{at}bio.sci.osaka-u.ac.jp
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