The FDF domain, so called because of the conserved FDF at its N termini, is an entirely alpha-helical domain with multiple exposed hydrophilic loops [1]. It is found at the C terminus of Scd6p-like SM domains [1][2]. It is also found with other divergent Sm domains and in proteins such as Dcp3p and FLJ21128, where it is found N terminal to the YjeF-N domain, a novel Rossmann fold domain [1].

1: Novel conserved domains in proteins with predicted roles in eukaryotic cell-cycle regulation, decapping and RNA stability. Anantharaman V, Aravind L; BMC Genomics. 2004;5:45. PMID:15257761

2: Novel Sm-like proteins with long C-terminal tails and associated methyltransferases. Albrecht M, Lengauer T; FEBS Lett 2004;569:18-26. PMID:15225602

3: Structural basis for the mutually exclusive anchoring of P body components EDC3 and Tral to the DEAD box protein DDX6/Me31B. Tritschler F, Braun JE, Eulalio A, Truffault V, Izaurralde E, Weichenrieder O; Mol Cell. 2009;33:661-668. PMID:19285948