Characterization of the sppA gene coding for protease IV, a signal peptide peptidase of Escherichia coli.

The sppA gene codes for protease IV, a signal peptide peptidase of Escherichia coli. Using the gene cloned on a plasmid, we constructed an E. coli strain carrying the ampicillin resistance gene near the chromosomal sppA gene and an sppA deletion strain in which the deleted portion was replaced by the kanamycin resistance gene. Using these strains, we mapped the sppA gene at 38.5 min on the chromosome, the gene order being katE-xthA-sppA-pncA. Although digestion of the signal peptide that accumulated in the cell envelope fraction was considerably slower in the deletion mutant than in the sppA+ strain, it was still significant, suggesting the participation of another envelope protease(s) in signal peptide digestion.