Crenactin
Crenactin is an actin homologue unique to the archaeal kingdom Crenarchaeota that has been found in the orders Thermoproteales and Candidatus Korarchaeum. It has the highest sequence similarity to eukaryotic actins of any known actin homologue. Crenactin has been well characterized in Pyryobaculum calidifontis and shown to have high specificity for ATP and GTP. Species containing crenactin are all rod or needle shaped and in P. calidifontis Crenactin has been shown to form helical structures that span the length of the cell, suggesting a role for crenactin in shape determination similar to that of MreB in other prokaryotes.
Read more about this topic: Prokaryotic Cytoskeleton