This domain is found on the N-terminal region of FKBPs such as FKBP25 and in the core region of E3 ubiquitin ligase HectD1. It adopts a compact 5-helix bundle, hence termed BTHB (Basic Tilted Helix Bundle) domain. In FKBP25, it has been suggested to have a role in regulating the association state of nucleosomes by interacting with nucleolin. Moreover, this basic domain in FKBP25 forms alternative complexes with other chromatin-related proteins, such as the HDAC1, HDAC2, and the transcriptional regulator YY1, the DNA binding activity of which is enhanced on binding FKBP25. Structural analysis of this fold suggests that the DNA binding properties of FKBP25 and HectD1 are presented by the conserved basic region [1].

1: Basic Tilted Helix Bundle - a new protein fold in human FKBP25/FKBP3 and HectD1. Helander S, Montecchio M, Lemak A, Fares C, Almlof J, Yi Y, Yee A, Arrowsmith C, DhePaganon S, Sunnerhagen M; Biochem Biophys Res Commun. 2014;447:26-31. PMID:24667607