We have identified a new locus, sodium 2 (sod2) based on selection for increased LiCl tolerance in fission yeast, Schizosaccharomyces pombe. Tolerant strains have enhanced pH‐dependent Na+ export capacity and sodium transport experiments suggest that the gene encodes an Na+/H+ antiport. The predicted sod2 gene product can be placed in the broad class of transporters which possess 12 hydrophobic transmembrane domains. The protein shows some sequence similarity to the human and bacterial Na+/H+ antiporters. Overexpression of sod2 increased Na+ export capacity and conferred sodium tolerance. Osmotolerance was not affected and sod2 cells were unaffected for growth in K+. In a sod2 disruption strain cells were incapable of exporting sodium. They were hypersensitive to Na+ or Li+ and could not grow under conditions that approximate pH7. The sod2 gene amplification could be selected stepwise and the degree of such amplification correlated with the level of Na+ or Li+ tolerance.
Deoxyribonucleic acids (DNA's) extracted from organisms presently placed in the genus Brucella (B. abortus, B. melitensis, B. neotomae, and B. suis) possessed very similar polynucleotide sequences. Unlabeled, single-stranded DNA fragments from B. abortus, B. melitensis, B. neotomae, and B. suis were equally effective in competing with the interaction of corresponding radiolabeled, single-stranded DNA fragments with their homologous DNA-agars. Unlabeled fragments of B. ovis, however, did not compete as effectively as the homologous, unlabeled DNA's, and this organism, therefore, had a detectably different polynucleotide composition. The mole percentages of guanine plus cytosine in Brucella DNA's (56 to 58 %) were also similar. DNA's from Francisella tularensis, Escherichia coli, and the slow loris did not compete.
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