CotC-CotU heterodimerization during assembly of the Bacillus subtilis spore coat

We report evidence that COW and COW, two previously identified components of the Bacillus subtilis spore coat, are produced concurrently in the mother cell chamber of the sporulating cell under the control Of sigma(K) and GerE and immediately assembled around the forming spore. In the coat, the two proteins interact to form a coat component of 23 kDa. The CotU-CotC interaction was not detected in two heterologous hosts, suggesting that it occurs only in B. subtilis. Monomeric forms of both COW and COW failed to be assembled at the surface of the developing spore and accumulated in the mother cell compartment of cells mutant for cotE. In contrast, neither COW nor COW accumulated in the mother cell compartment of cells mutant for cotH. These results suggest that CotH is required to protect both COW and COW in the mother cell compartment of the sporangium and that CotE is needed to allow their assembly and subsequent interaction at the spore surface.