Vestiges of the Bacterial Signal Recognition Particle-Based Protein Targeting in Mitochondria

Abstract The main bacterial pathway for inserting proteins into the plasma membrane relies on signal recognition particle (SRP), composed of Ffh protein and an associated RNA component, SRP-docking FtsY. Eukaryotes use equivalent system archaeal origin to deliver endoplasmic reticulum, whereas a bacteria-derived SRP FtsY function in plastid. Here we report presence homologs various unrelated plastid-lacking unicellular eukaryotes, namely Heterolobosea, Alveida, Goniomonas, Hemimastigophora. monophyly novel eukaryotic groups, predicted mitochondrial localization experimentally confirmed Naegleria gruberi, strong alphaproteobacterial affinity group, collectively suggest that they constitute parts ancestral peptide-based protein-targeting inherited from last common ancestor, but lost majority extant eukaryotes. ability putative peptides, subset mitochondrial-encoded N. gruberi proteins, target reporter fluorescent reticulum Trypanosoma brucei, likely through their interaction with cytosolic SRP, provided further support this notion. We also illustrate known ribosome-interacting implicated targeting opisthokonts (Mba1, Mdm38, Mrx15) are broadly conserved eukaryotes nonredundant system. Finally, identified (MAP67) present diverse related peptide-binding domain Ffh, which may well be hitherto unrecognized component machinery.