SecA2 domains were identified by alignment with E. coli SecA. Domain boundaries are based on those determined by Papanikolau et al [4]. NBD, nucleotide binding domain; PPXD, preprotein cross-linking domain; HWD, helical wing domain; HSD, helical scaffold domain; IRA, intramolecular regulator of ATPase activity; CTD, C-terminal domain. IRA1 is a functional domain that overlaps with the two-helix finger structural domain [6, 97]. Numbers shown below the SecA2 proteins indicate the percent similarity/identity with the corresponding domain of the SecA paralogue.