This domain is found in the FtsH family of proteins. FtsH is the only membrane-bound ATP-dependent protease universally conserved in prokaryotes ([1]). It only efficiently degrades proteins that have a low thermodynamic stability - e.g. it lacks robust unfoldase activity. This feature may be key and implies that this could be a criterion for degrading a protein. In Oenococcus oeni FtsH is involved in protection against environmental stress ([2]), and shows increased expression under heat or osmotic stress. These two lines of evidence suggest that it is a fundamental prokaryotic self-protection mechanism that checks if proteins are correctly folded (personal obs: Yeats C). The precise function of this N-terminal region is unclear.

1: Lack of a robust unfoldase activity confers a unique level of substrate specificity to the universal AAA protease FtsH. Herman C, Prakash S, Lu CZ, Matouschek A, Gross CA; Mol Cell 2003;11:659-669. PMID:12667449

2: The ftsH gene of the wine bacterium Oenococcus oeni is involved in protection against environmental stress. Bourdineaud JP, Nehme B, Tesse S, Lonvaud-Funel A; Appl Environ Microbiol 2003;69:2512-2520. PMID:12732516