Structure and assembly of the bacterial endospore coat

Many biological processes are mediated through the action of multiprotein c omplexes, often assembled at specific cellular locations. Bacterial endospo res for example, are encased in a proteinaceous coat, which confers resista nce to lysozyme and harsh chemicals and influences the spore response to ge rminants. In Bacillus subtilis, the coat is composed of more than 20 polype ptides, organized into three main layers: an amorphous undercoat; a lamella r, lightly staining inner structure; and closely apposed to it, a striated electron-dense outer coat. Synthesis of the coat proteins is temporally and spatially governed by a cascade of four mother cell-specific transcription factors. However, the order of assembly and final destination of the coat structural components may rely mainly on specific protein-protein interacti ons, as well as on the action of accessory morphogenetic proteins. Proteoly tic events, protein-protein crosslinking, and protein glycosylation also pl ay a role in the assembly process. These modifications are carried out by e nzymes that may themselves be targeted to the coat layers. Coat genes have been identified by reverse genetics or, more recently, by screens for mothe r cell-specific promoters or for peptide sequences able to interact with ce rtain bait proteins. A role for a given locus in coat assembly is establish ed by a combination of regulatory, functional, morphological, and topologic al criteria. Because of the amenability of B. subtilis to genetic analysis (now facilitated by the knowledge of its genome sequence), coat formation h as become an attractive model for the assembly of complex macromolecular st ructures during development. (C) 2000 Academic Press.