Biosynthesis of Antibiotic U-22,324, a Cyclic Polypeptide

Antibiotic U-22,324 is a polypeptide produced by the fungus Trichoderma viride. Cycloheximide was found to block gross cellular protein synthesis of T. viride with little interference with antibiotic synthesis. No radioactive label was recovered in the ribosomes when labeled amino acids and cycloheximide were added to a culture at the onset of peptide synthesis although net antibiotic synthesis took place under these conditions. The cell-bound antibiotic portion was exclusively localized within the gross cellular debris fraction. This suggests that antibiotic U-22,324 is not synthesized on ribosomes but by an extraribosomal peptide synthetic mechanism similar to the one proposed for bacterial peptide antibiotics, toxins, and cell wall components.