CLONING, NUCLEOTIDE-SEQUENCE AND EXPRESSION IN STREPTOMYCES-LIVIDANS AND ESCHERICHIA-COLI OF PABB FROM LACTOCOCCUS-LACTIS SUBSP LACTIS NCDO-496

A gene (pabB) encoding the aminase activity of p-aminobenzoate (PABA) synthase in Lactococcus lactis subsp. lactis was cloned in pIJ41 and e xpressed in Streptomyces lividans strains defective in PABA biosynthes is. Expression of the gene was associated with a 1.2 kb deletion betwe en the aph promoter and the cloning site in pIJ41. Subcloning in pBR32 2 and expression in Escherichia coli AB3295 of the cloned L. lactis DN A fragment localized the pabB-complementing gene in a 1.9 kb segment. The nucleotide sequence of this segment contained a 1410 bp open readi ng frame encoding a 470-amino-acid polypeptide of 50937 Da. The deduce d amino acid sequence showed substantial similarity to those reported for PabB and TrpE from several organisms. Synonymous codon usage refle cted the low G + C content in the genomic DNA of L. lactis subsp. lact is, and therefore differed markedly from the preferred usage in the S. lividans host. The cloned heterologous pabB DNA was expressed in amou nts that allowed accumulation of excreted PABA in cultures of S. livid ans transformants.