Alignment of 937 sequences representing the SRP system used in this study processed in Gblocks.

Sequence names follow the format gene_domain_phylum_Accession#, where gene refers to either FtsY, Ffh, FlhA or the secretion system (SS), domains and phyla or superphyla are according to NCBI taxonomy, and accession numbers are from the NCBI nr protein database. Note that the sequence SS_Archaea_TACK_TBR20608 is present in the ungapped alignment (S3 File and Fig 2) but not the alignment processed in Gblocks, which led to the removal of all sites containing this sequence. (TXT)