The saccharomicins A and B, produced by the actinomycete Saccharothrix espanaensis, are oligosaccharide antibiotics. They consist of 17 monosaccharide units and the unique aglycon N-(m,p-dihydroxycinnamoyl)taurine. To investigate candidate genes responsible for the formation of trans-m,p-dihydroxycinnamic acid (caffeic acid) as part of the saccharomicin aglycon, gene expression experiments were carried out in Streptomyces fradiae XKS. It is shown that the biosynthetic pathway for trans-caffeic acid proceeds from L-tyrosine via trans-p-coumaric acid directly to trans-caffeic acid, since heterologous expression of sam8, encoding a tyrosine ammonia-lyase, led to the production of trans-p-hydroxycinnamic acid (coumaric acid), and coexpression of sam8 and sam5, the latter encoding a 4-coumarate 3-hydroxylase, led to the production of trans-m,p-dihydroxycinnamic acid. This is not in accordance with the general phenylpropanoid pathway in plants, where trans-pcoumaric acid is first activated before the 3-hydroxylation of its ring takes place.Saccharothrix is a genus of gram-positive bacteria belonging to the well-known order Actinomycetales. Most agents used at present for the treatment of bacterial infections were discovered in members of the Actinomycetales. Saccharothrix espanaensis produces the two heptadecaglycoside antibiotics saccharomicins A and B, which represent a new class of antibiotics (15, 18). They exhibit potent antibacterial activity both in vitro and in vivo against multiply-resistant strains of Staphylococcus aureus as well as vancomycin-resistant enterococci (25). The saccharomicins consist of an oligosaccharide portion and the intriguing aglycon N-(m,p-dihydroxycinnamoyl)taurine (Fig. 1), in which caffeic acid is linked to the amino sulfonic acid taurine via an amide bond.Enzymes belonging to the group of ammonia-lyases catalyze the conversion of ␣-amino acids into ␣,␤-unsaturated acids by elimination of ammonia. Ubiquitous in plants and fungi, phenylalanine ammonia-lyase (PAL) (EC 4.3.1.5) catalyzes the nonoxidative deamination of the primary amino acid L-phenylalanine to trans-cinnamic acid (trans-cinnamate), which is the first reaction of the so-called general phenylpropanoid pathway in plants (8). Phenylpropanoids include several important natural product classes, for example, flavonoids, lignins, and coumarins. In monocotyledons, PAL utilizes L-tyrosine in addition to L-phenylalanine (resulting in trans-p-coumaric acid), whereas the enzyme from dicotyledons converts only L-phenylalanine sufficiently. Both PAL and tyrosine ammonia-lyase (TAL) activity are very rare in bacteria (17, 30).The next reactions of the three-step general phenylpropanoid pathway are catalyzed by the enzymes trans-cinnamate 4-monooxygenase (also called cinnamate 4-hydroxylase; EC 1.14.13.11), leading to trans-p-coumaric acid (trans-4-coumarate), and 4-coumarate-coenzyme A (CoA) ligase (EC 6.2.1.12), leading to 4-coumaroyl-CoA (8).In this report, we describe the cloning and identification of two genes from S. espanaensis w...

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