Primary structure of the plasma membrane H(+)-ATPase from the halotolerant alga Dunaliella bioculata.

P-type ATPase-specific oligodeoxyribonucleotides were used to obtain a fragment of the H(+)-ATPase of the salt tolerant alga Dunaliella bioculata by polymerase chain reaction (PCR). This fragment served as a probe in screening a cDNA-library from this organism. The complete primary structure of the ATPase protein (DBPMA1) was deduced from sequencing a 4.7 kb cDNA clone. The protein shows highest homology to H(+)-ATPases from higher plants and fungi (43% identity, 67% similarity) but has a higher calculated molecular mass (123 kDa). The latter can be assigned mainly to an additional hydrophilic domain between transmembrane segments VI and VII and to an extended carboxyterminus. These unusual structural features of DBPMA1 are interpreted in terms of providing regulatory sites of the enzyme. Southern blot analysis suggests the presence of only a single copy of the gene in the haploid D. bioculata genome. To investigate the role of the H(+)-ATPase in the adaption of D. bioculata to different external NaCl concentrations, we employed northern blot analyses. The results indicate that the pma1 transcript level of cells growing in salinities between 0.1 and 3 M NaCl is not directly correlated with the external salt concentration.