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.