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.

Gassericin A, a bacteriocin produced by Lactobacillus gasseri LA39, has a cyclic structure linking N-and C-terminal amino acids. Gassericin A was expressed in Escherichia coli JM109 as a biotinylated fusion protein on the basis of the DNA sequence of mature bacteriocin. A positive clone accumulated the bacteriocin, with no activity, as a soluble fusion protein in the cytoplasm. After release of an N-terminal tag with factor Xa protease, gassericin A was converted into an active peptide having N-and C-termini. The total amount of purified bacteriocins (expressed and native) was 480 m g/L and 370 m g/L, respectively. However, the specific activity of expressed gassericin A was 15 AU/mg lower than that of native bacteriocin (2600 AU/mg). Although the actual Mr (molecular weight) of the expressed bacteriocin should be 5666, the peptide showed the same mobility (Mr 3800) in sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) as native cyclic gassericin A, suggesting that the expressed peptide retains compact folding of the molecule similar to that of native gassericin A.