Cleaves the spore coat proteins SpoIVA and SafA. May cooperate with tgl to mediate the temperature-dependent cross-linking of coat proteins like GerQ. Synthesized in the mother cell compartment and assembled on the surface of the forespore. Expressed in the mother cell compartment from T4 of sporulation. Induced by SigK. According to PubMed:10714992, cells have an altered coat protein composition; CotT, YeeK, YxeE, CotF, SafA and SpoIVA proteins are present at increased levels and/or exist as precursors. According to PubMed:16751597, cells show no effects on vegetative growth or spore resistance to heat, chloroform or lysozyme. The germination of YabG mutant spores in L-alanine and in a mixture of L-asparagine, D-glucose, D-fructose and potassium chloride was the same as that of the wild-type spores. Heat treatment for 20 minutes at 60 degrees Celsius, which maximally activates the Tgl enzymatic activity, causes cross-linking of GerQ in isolated YabG-deleted spores but not in Tgl/YabG double-mutant spores. Additionally, the germination frequency of the Tgl/YabG double-mutant spores in the presence of L-alanine with or without heat activation at 60 degrees Celsius is lower than that of wild-type spores. Belongs to the peptidase U57 family.