This domain is found in the FtsH family of proteins. FtsH is the only membrane-bound ATP-dependent protease universally conserved in prokaryotes. 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, 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.