Expression, localization and modification of YxeE spore coat protein in Bacillus subtilis.

YxeE is a spore coat protein of Bacillus subtilis. We have previously reported that YxeE can be extracted from yabG mutant spores. In the present study, we analysed the expression and localization of YxeE. Northern analysis detected the transcript of yxeE from sporulating cells 4 h after the onset of sporulation, and revealed that the synthesis of yxeE mRNA was dependent on expression of the SigK RNA polymerase and the GerE regulator. Immunoblotting with anti-YxeE antiserum detected YxeE from sporulating cells 4 h after the onset of sporulation. YxeE was detected in the extracts from mature spores of yabG mutant strain but not in those from wild-type spores. On the other hand, fluorescence microscope observations showed that YxeE-green fluorescent protein (GFP) is located at the surface of both wild-type and yabG spores. Immunoblot analysis with anti-GFP antiserum showed that YxeE-GFP was not digested in yabG-disrupted strain and that only the GFP portion remained in the wild-type yabG background. We conclude that YxeE is a substrate of YabG protease.