This is the N-terminal domain found in Stage II sporulation protein E which includes the 10 transmembrane domains and the regulatory domain, the latter located adjacent the PP2C phosphatase domain. The regulatory domain mediates the formation of dimers between SpoIIE molecules, required for phosphatase activation [1]. An N-terminal 45-residue long alpha-helix makes intramolecular contacts with the switch helices (alpha1 and alpha2) of the phosphatase domain [1].

1: A widespread family of serine/threonine protein phosphatases shares a common regulatory switch with proteasomal proteases. Bradshaw N, Levdikov VM, Zimanyi CM, Gaudet R, Wilkinson AJ, Losick R; Elife. 2017; [Epub ahead of print] PMID:28527238