Members of this family, which are found in a set of hypothetical bacterial proteins, contain a core of six alpha-helices, where one central helix is surrounded by the other five. The exact function of this family has not, as yet, been determined [1]. The known structure shows this domain contains two copies of the histone fold [1].

1: The crystal structure of Aq_328 from the hyperthermophilic bacteria Aquifex aeolicus shows an ancestral histone fold. Qiu Y, Tereshko V, Kim Y, Zhang R, Collart F, Yousef M, Kossiakoff A, Joachimiak A; Proteins. 2006;62:8-16. PMID:16287087