In eukaryote, the Nascent polypeptide-Associated Complex (NAC) is a heterodimeric cytosolic protein complex composed of NAC α and NAC β. NAC binds reversibly to the ribosome where it is in contact with nascent chains as they emerge from the ribosome. But the cellular function of NAC seems to be much more diverse as it is also involved in transcription regulation and mitochondrial translocation [1]. α and β NACs share homology with each other, both contain a NAC A/B domain. In archaea no β NAC proteins are found; the complex is an homodimer of NAC α [2,3].

The crystal structure of an archeal NAC has been solved (see <PDB:1TR8>) [3]. The NAC A/B domain consists of six strands arranged in a β barrel structure similar to the OB fold. Various OB folds interact with ribosomal RNA which could suggest a similar role for the NAC A/B domain.

The profile we developed covers the whole NAC A/B domain.