FIG. 1.

Sequence alignment of putative signal peptide peptidase proteins from E. coli, B. subtilis, and representative archaeal strains. The 19 archaeal SppA sequences described in Fig. 2 were aligned with the sequences of SppA from E. coli and B. subtilis. After alignment, representative sequences were selected. Asterisks indicate highly conserved residues that were present in at least 18 of the 21 sequences aligned. Among these, residues that were conserved in all sequences examined are indicated by stars. The bar above the alignment indicates the putative transmembrane domain of signal peptide peptidase from T. kodakaraensis. Arrowheads indicate the residues that immediately follow the artificial Met residue incorporated in ΔN29SppA_Tk and ΔN54SppA_Tk. Tko, T. kodakaraensis; Mja, Methanocaldococcus jannaschii; Tac, Thermoplasma acidophilum; PaI, Pyrobaculum aerophilum I; Neq, Nanoarchaeum equitans; Hba, Halobacterium sp. strain NRC-1; Bsp, B. subtilis; Eco, E. coli. Due to their lengths, not all residues are shown for Pyrobaculum aerophilum I (608 residues), Halobacterium sp. strain NRC-1 (300 residues), and E. coli (618 residues).