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Germination of Bacillus subtilis spores via the GerA nutrient receptor was suppressed by GerAC lacking the diacylglycerylated cysteine essential for receptor function. Spores of Bacillus species are metabolically dormant and can remain so for long periods of time. However, nutrient receptors located in the dormant spore's inner membrane can sense the presence of exogenous nutrients and trigger the process of spore germination that leads to a resumption of metabolism in spore outgrowth 7 , 13 , 14 , 15 , 20 , 21 , There are three functional nutrient receptors in Bacillus subtilis spores, the products of the homologous tricistronic gerA , gerB , and gerK operons termed gerA operon homologs 13 , 14 , 15 , 21 , 25 , Based on their amino acid sequences, the A and B proteins encoded by gerA operon homologs are most likely integral membrane proteins 13 , 21 , The third encoded protein, C, is probably not an integral membrane protein, but the C proteins have a signal peptide followed by a consensus sequence for diacylglycerol addition to a cysteine residue and a signal peptidase II cleavage site 8 , 13 , 21 , 23 , Consequently, it is likely that some combination of the signal peptide and diacylglycerol addition ensures that the C proteins are also in the spore's inner membrane.
The addition of diacylglycerol to the C proteins of GerA receptor homologs is important for receptor function, as loss of the only B. The lack of diacylglycerol addition to C proteins almost completely eliminates the function of the GerA receptor that responds to l -alanine, significantly but not completely abolishes spore germination via the GerB receptor, but has little effect on germination via the GerK receptor 8.
The presence of genes for the A, B, and C proteins of GerA receptor homologs in an operon suggests that each receptor is a complex of the appropriate A, B, and C proteins, and loss of any cistron of a particular gerA operon homolog eliminates the function of the encoded receptor 13 , 14 , However, there is no evidence for the physical interaction of the C protein with the A and B proteins of either of these receptors.
It was shown recently that substitution of alanine for the diacylglycerylated cysteine residue in GerAC residue 18 or GerBC residue 20 reduces GerA and GerB receptor function and 7-fold, respectively 8.
