The atp operon of alkaliphilic Bacillus pseudofirmus OF4, as in most prokaryotes, contains the eight structural genes for the F-ATPase (ATP synthase), which are preceded by an atpI gene that encodes a membrane protein with 2 TMSs. A tenth gene, atpZ, has been found in this operon, which is upstream of and overlapping with atpI. AtpI is a Ca2+/Mg2+ transporter [3].

1: Structure and function of H+-ATPase: what we have learned from Escherichia coli H+-ATPase. Kanazawa H, Futai M; Ann N Y Acad Sci 1982;402:45-64. PMID:6301339

2: Bacillus subtilis F0F1 ATPase: DNA sequence of the atp operon and characterization of atp mutants. Santana M, Ionescu MS, Vertes A, Longin R, Kunst F, Danchin A, Glaser P; J Bacteriol 1994;176:6802-6811. PMID:7961438

3: A tenth atp gene and the conserved atpI gene of a Bacillus atp operon have a role in Mg2+ uptake. Hicks DB, Wang Z, Wei Y, Kent R, Guffanti AA, Banciu H, Bechhofer DH, Krulwich TA; Proc Natl Acad Sci U S A. 2003;100:10213-10218. PMID:12917488