The carboxyl terminus of the Bacillus subtilis SecA is dispensable for protein secretion and viability

The Escherichia coli secretion-dedicated chaperone SecB targets a subset of proteins to the translocase by interacting with the carboxyl (C-) terminus of SecA. This region of SecA is highly conserved in Eubacteria, but despit e its presence in the Bacillus subtilis SecA, the B. subtilis genome does n ot appear to contain a gene for a clear homologue of SecB. Deletion of the C-terminus of the B. subtilis SecA yields cells that have normal viability, but that exhibit a response reminiscent of oxidative stress and the loss o f a number of secretory proteins from the culture supernatant. Semi-quantit ative RT-PCR demonstrates that these proteins are expressed at lower levels . The C-terminus of SecA fused to glutathione S-transferase (GST) specifica lly binds a cytosolic protein, termed MrgA. This protein has been reported to function in relation to oxidative stress, but deletion of the mrgA gene does not result in a secretion defect nor does it cause an oxidative stress response. It is concluded that the C-terminus of the B. subtilis SecA is n ot essential for secretion and viability.