Along with the bacABCDEF operon, BacG is involved in the biosynthesis of the nonribosomally synthesized dipeptide antibiotic bacilysin, composed of L-alanine and L-anticapsin. Bacilysin is an irreversible inactivator of the glutaminase domain of glucosamine synthetase (PubMed:20052993). BacG catalyzes the stereoselective reduction of exocyclic-delta(3),delta(5)-dihydro-hydroxyphenylpyruvate (ex-H2HPP), adding a pro-S hydride equivalent to C4 position to yield tetrahydro-hydroxyphenylpyruvate (H4HPP) (PubMed:22765234, PubMed:23519407). Although the 3Z,7R-ex-H2HPP isomer is kinetically disfavored by BacB and produced in a smaller quantity than 3E,7R-ex-H2HPP, it is the preferred substrate for the conjugate reduction reaction of BacG (PubMed:22765234, PubMed:23519407). kcat is 71.3 min(-1) for reductase activity with 3Z,7R-ex-H2HPP as substrate. kcat is 33.2 min(-1) for reductase activity with 3E,7R-ex-H2HPP as substrate. kcat is 34.38 sec(-1) for reductase activity with ex-H2HPP as substrate. Antibiotic biosynthesis; bacilysin biosynthesis. Homodimer. The compound guanosine 5'-diphosphate 3'-diphosphate (ppGpp) is essential for the transcription of the bacABCDEF operon and BacG, and GTP regulates the transcription of both this operon and ywfH via the CodY-mediated regulation system. Belongs to the short-chain dehydrogenases/reductases (SDR) family.