The original family covered both the regions found by the current model. The splitting of the family has allowed the related FlaJ_arch (archaeal FlaJ family) to be merged with it. Proteins with this domain in form a platform for the machiney of the Type II secretion system, as well as the Type 4 pili and the archaeal flagella [1]. This domain seems to show some similarity to PF00664 but this may just be due to similarities in the TM helices (personal obs: C Yeats).

1: An inner membrane platform in the type II secretion machinery of Gram-negative bacteria. Py B, Loiseau L, Barras F; EMBO Rep 2001;2:244-248. PMID:11266368

2: The general secretory pathway: a general misnomer?. Desvaux M, Parham NJ, Scott-Tucker A, Henderson IR; Trends Microbiol. 2004;12:306-309. PMID:15223057

3: Type II protein secretion and its relationship to bacterial type IV pili and archaeal flagella. Peabody CR, Chung YJ, Yen MR, Vidal-Ingigliardi D, Pugsley AP, Saier MH Jr; Microbiology. 2003;149:3051-3072. PMID:14600218

4: Secretion and subcellular localizations of bacterial proteins: a semantic awareness issue. Desvaux M, Hebraud M, Talon R, Henderson IR; Trends Microbiol. 2009;17:139-145. PMID:19299134