SEQUENCING AND CHARACTERIZATION OF THE NTP GENE-CLUSTER FOR VACUOLAR-TYPE NA-TRANSLOCATING ATPASE OF ENTEROCOCCUS-HIRAE()

We have previously reported the DNA and amino acid sequences for the t hree genes (ntpA, ntpB, and ntpK) encoding the A, B, and K (proteolipi d) subunits, respectively, of Na+-translocating ATPase of a eubacteriu m Enterococcus hirae (Kakinuma, Y., Kakinuma, S., Takase, K., Konishi, K., Igarashi, K., and Yamato, I. (1993) Biochem. Biophys. Res. Commun . 195,1063-1069). In this paper we report the entire nucleotide sequen ce of the ntp gene cluster coding for this multisubunit enzyme. The cl uster contained eight other genes; the order of these 11 genes was ntp F, -I, -K, -E, -C, -G, -A, -B, -D, -H, and -J, encoding proteins with predicted molecular weights of 14,255, 75,619, 16,036, 22,699, 38,162, 11,409, 65,766, 51,139, 27,093, 7,164, and 48,869, respectively. The deduced amino acid sequences of these products suggested that NtpI and NtpJ are hydrophobic proteins and others are hydrophilic. The ntpI ge ne product, which possesses six membrane-spanning segments in its carb oxyl-terminal half, resembled the 116-kDa subunit of vacuolar (V)-ATPa se in clathrin-coated vesicles. In addition, the NtpE, NtpC, NtpG, and NtpD proteins resembled bovine kidney ATPase E subunit, Saccharomyces cerevisiae Vma6p, Manduca sexta V-ATPase 14-kDa subunit, and Sulfolob us acidocaldarius gamma subunit, respectively, although the similariti es between their amino acid sequences were moderate. Other gene produc ts (NtpF and NtpH) did not show significant sequence similarity to oth er V-ATPase subunits. Since NtpA, NtpB, and NtpK are homologous counte rparts of V-ATPase, these findings suggest that the molecular architec ture of E. hirae Na+-ATPase complex corresponds to the V-type H+-ATPas e complex distributed in various eukaryotic endomembrane systems. The sequence of the NtpJ product was similar to those of K+ transport syst ems of S. cerevisiae (Trk1 and Trk2); its meaning will be discussed. T his is the first demonstration of a eukaryotic V-ATPase-like Na+ pump in bacteria.