Bacillus subtilis spore coat

In response to starvation, bacilli and clostridia undergo a specialized pro gram of development that results in the production of a highly resistant do rmant cell type known as the spore. A proteinacious shell, called the coat, encases the spore and plays a major role in spore survival. The coat is co mposed of over 25 polypeptide species, organized into several morphological ly distinct layers. The mechanisms that guide coat assembly have been large ly unknown until recently. We now know that proper formation of the coat re lies on the genetic program that guides the synthesis of spore components d uring development as well as on morphogenetic proteins dedicated to coat as sembly. Over 20 structural and morphogenetic genes have been cloned. In thi s review, we consider the contributions of the known coat and morphogenetic proteins to coat function and assembly. We present a model that describes how morphogenetic proteins direct coat assembly to the specific subcellular site of the nascent spore surface and how they establish the coat layers. We also discuss the importance of posttranslational processing of coat prot eins in coat morphogenesis. Finally, we review some of the major outstandin g questions in the field.