Stability of structures of the epsilon subunit and terminator of thermophilic ATPase

F1-type ATPase is the central enzyme for ATP synthesis in most organisms. Because of the extreme reconstitutability of thermophilic ATPase (TF1) and diversity of the minor subunits of F1 type ATPase, an operon coding for TF1 was isolated from DNA of thermophilic bacterium PS3, and its terminal region containing the epsilon subunit (TF1 epsilon) and terminator was sequenced. The primary structure of the epsilon subunit (Mr = 14 333) was deduced from the nucleotide sequence (396 base-pairs) and amino-acid sequence of its amino terminus. The conclusions drawn from the results are as follows. Homologies: TF1 epsilon shows only 6% homology with the epsilon subunits of eight species reported, but 50% homology with Escherichia coli epsilon and 41% with chloroplast. The residues having a tendency to form reverse turns (Gly, Pro and Tyr) and His are relatively well conserved. Unlike some F1 epsilon types TF1 epsilon has no ATPase inhibitor activity and is not homologous with ATPase inhibitor. TF1 epsilon is essential to connect F1 to F0, like the b subunit, and is weakly homologous with the b subunit of F0F1. The cause of 3 beta: 1 epsilon subunit stoichiometry: The ribosome binding sequence of TF1 epsilon is TAGGN7, which is incomplete compared with that of TF1 beta. The codon usage for TF1 epsilon is similar to that for TF1 epsilon. The cause of stability of TF1 epsilon and its gene: There are 18 ionic groups at the putative reverse turns and the N- and C-termini of TF1 epsilon, but only 10 ionic groups in the corresponding sites of E. coli epsilon subunit. These ionic groups enhance the external polarity of TF1 epsilon and may intensify subunit-subunit interaction. There is a terminator at the 3' end of the TF1 epsilon gene, which is stabilized by a long (13 base-pairs) stem.