Alignment of two gene clusters related to the P. horikoshii OT3 protein-protein interactions. All the gene clusters were obtained using the Sequence Similarity Database (SDDB)  gene cluster search of the Kyoto Encyclopedia of Genes and Genomes (KEGG) [48,49]. (a) The gene cluster encoding archaeal- or vacuolar-type H+-ATP synthase protein subunits. The arrow shows the P. horikoshii protein interaction pair PH1983 and PH1978. The structure model (inset) was derived from Methanococcus jannaschii . (b) The gene cluster encoding SNO/SNZ family proteins similar to PH1354 and PH1355. The black and gray open reading frames correspond to SNO and SNZ proteins, respectively.