Graduation date: 2006Molecular genetic and enzymological techniques have been employed to study antibiotic biosynthesis. In this thesis, we studied the formation and modification of the nonproteinogenic amino acid enduracididine (End), which exists in two important antibiotics, mannopeptimycins (MPPs) and enduracidin. Sequence analysis of the MPP gene cluster revealed that the product of mppO belongs to His-3 variant of non-heme iron, α-ketoglutarate dependent oxygenase superfamily. The mppO gene was subcloned and heterologously expressed in E. coli. Enzyme activity assays showed that MppO stereospecifically catalyzes hydroxylation of the β-carbon of L-End and results in the formation of 3S-hydroxy-L-End. MppO is the first known enzyme that catalyzes the β-hydroxylation of a nonproteinogenic amino acid. The formation of enduracididine was also studied in the enduracidin biosynthesis pathway. Three genes in the end cluster, endP, endQ and endR are predicted to be involved in the formation of L-End. The gene products of endP and endQ are proposed to be pyridoxal phosphate (PLP)-dependent enzymes. These genes were subcloned and expressed in E. coli. A fragment containing the whole endPQR operon was introduced into S. lividans and S. fungicidicus. Two possible mechanisms of enduracididine formation were proposed with β-OH-L-Arg or γ-OH-L-Arg as precursor, respectively.