This superfamily represents a domain covering the whole length of the nuclear transport factor 2 (NTF2). It has a beta-alpha(2)-beta insertion after the main helix. Ntf2 protein is a nuclear envelope protein facilitating protein transport into the nucleus.Besides Ntf2, proteins containing this domain include protein kinases, sucrose phosphatases, bacterial ring-hydroxylating dioxygenase beta subunit, protein NXF and many other uncharacterised proteins.