A gene encoding H^+-ATPase of ruminal bacteria, Ruminococcus albus and Streptococcus bovis, was cloned and the entire operon (atp) was sequenced by the inverse PCR method. The atp operon of S.bovis was found to be approximately 6.5 kbp, which consisted of atp E (c-subunit), B (a), F (b), H (delta), A (alpha), G (gamma), D (beta), and C (epsilon) in this order. In the atp operon of R.albus, the order of atp E and B was inversed, and in addition assumed atp I (i) was included. The open reading frame was approximately 7 kbp.
Primer extension analysis was conducted for the atp operon of S.bovis with the result indicating the presence of three different species of atp-mRNA.The proportion of each mRNA species was different in S.bovis cells grown at pH 4.7 compared to those grown at pH 7.0. This suggests that the synthesis of H^+-ATPase is regulated at the transcriptional or post-transcriptional level.