Escherichia coli FtsH is an essential integral membrane protein that has an AAA-type ATPase domain at its C-terminal cytoplasmic part, which is homologous to at least three ATPase subunits of the eukaryotic 26S proteasome. We report here that FtsH is involved in degradation of the heat-shock transcription factor a32, a key element in the regulation of the E.coli heat-shock response. In the temperature-sensitive ftsHJ mutant, the amount of aY32 at a non-permissive temperature was higher than in the wild-type under certain conditions due to a reduced rate of degradation. In an in vitro system with purified components, FtsH catalyzed ATPdependent degradation of biologically active histidinetagged &32. FtsH has a zinc-binding motif similar to the active site of zinc-metalloproteases. Protease activity of FtsH for histidine-tagged a32 was stimulated by Zn2+ and strongly inhibited by the heavy metal chelating agent o-phenanthroline. We conclude that FtsH is a novel membrane-bound, ATP-dependent metalloprotease with activity for a32. These findings indicate a new mechanism of gene regulation in E.coli.

Among the variety of specialized intercellular junctions, those of the adherens type have the most obvious association with cytoskeletal elements. This may be with the actin microfilanent system as in the zonula adherens or with intermediate ifiaments as in the macula adherens, or desmosome. In the former case, it is clear that transmembrane glycoproteins of the cadherin family are important adhesive components of the molecular assembly. We now show for desmosomes that a major glycoprotein component (desmosomal glycoprotein DGI) has extensive homology with the cadherins, defining an extended fmily, but also has unique features in its cytoplasmic domain that are likely to be relevant to the association with intermediate rather than actin filaments. A novel 282-residue extension contains repeats of --29 amino acid residues predicted to have an antiparallel P-sheet structure, followed by a glycine-rich sequence. As in the cadherins, the extracellular domain contains possible Ca2+-binding sequences and a potential protease processing site. The cell adhesion recognition region (His-Ala-Val) METHODSGeneration and Screening ofAntibodies. Desmosomes were isolated from bovine muzzle epidermis (4). Rabbit anti-DGI serum was generated against DGI purified by SDS/PAGE and electroelution; its specificity was similar to the guinea pig sera previously described (4). The tTo whom reprint requests should be addressed. §The sequence reported in this paper has been deposited in the GenBank data base (accession no. X56654). 4796The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Part of the cytoplasmic domain of a human desmoglein, Dsgl, a cadherin-like protein found in desmosomes of epithelial cells, has been visualised by electron microscopy. The cloned fragment contains five repeats of a 29 + 4 residue sequence unique to desmogleins, followed by a glycine-rich region. In rotary shadowed preparations the molecule consists of a globular head attached to a thin tail, the latter perhaps corresponding to the glycine-rich region. This portion of the molecule is thought to span the width of the inner dense plaque. The structure and dimensions concur well to the configuration deduced from the protein sequence.