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The Streptomyces viridochromogenes peptide synthetase gene, phsA has no surrounding peptide antibiotic encoding genes. The gene encodes a protein with 622 amino acids. The carboxy terminal of the PhsA protein is essential for the peptide synthetase activity. The gene is involved in the production of phosphinothricin tripeptide. PhsA is necessary for the activation and condensation of one amino acid. Fragments of the phsA gene cloned into pGM vectors integrate into the phsA gene or outside the phsA locus in gene disrupted mutants.

Streptomyces viridochromogenes Tü494 produces the antibiotic phosphinothricyl-alanyl-alanine (Ptt). Ptt-non-producing mutants were isolated following N-methyl-N'-nitro-N-nitrosoguanidine (NTG) or UV light treatment of spore suspensions. In co-synthesis and bioconversion experiments the mutational blocks in the biosynthetic pathway were localized. The mutant NTG1 was analysed in detail. This mutant acts as a secretor for all other mutants. From bioconversion experiments with presumptive precursors circumstantial evidence was obtained that NTG1 is mutated in a gene involved in the alanylation of N-acetyl-demethyl-phosphinothricin. Using a cosmid gene library the DNA region complementing the defective gene of mutant NTG1 was isolated on a 4-kb BamHI fragment. Subcloning experiments showed that a 3-kb BglII/BamHI fragment is sufficient for complementation of mutant NTG1.