SUBCELLULAR-LOCALIZATION OF PROTEINS INVOLVED IN THE ASSEMBLY OF THE SPORE COAT OF BACILLUS-SUBTILIS

Spores of the bacterium Bacillus subtilis are encased in a two-layered protein shell, which consists of an electron-translucent, lamellar in ner coat, and an electron-dense outer coat. The coat protein CotE is b oth a structural component of the coat and a morphogenetic protein tha t is required for the assembly of the outer coat. We now show that Cot E is located in the outer coat of the mature spore and that at an inte rmediate stage of sporulation, when the developing spore (the forespor e) is present as a free protoplast within the sporangium, CotE is loca lized in a ring that surrounds the forespore but is separated from it by a small gap. We propose that the ring is the site of assembly of th e outer coat and that the gap is the site of formation of the inner co at. Assembly of the ring depends on the sporulation protein SpoIVA, wh ich sits close to or on the surface of the outer membrane that encircl es the forespore. We propose that SpoIVA creates a basement layer arou nd the forespore on which coat assembly takes place. The subcellular l ocalization and assembly of CotE and other coat proteins are therefore determined by the capacity of SpoIVA to recognize and adhere to a spe cific surface within the sporangium, the outer membrane of the forespo re.