U-42, 126, a new antimetabolite antibiotic: production, biological activity, and taxonomy of the producing microorganism.

A new antimetabolite antibiotic, U-42,126, was discovered by use of a specific in vitro screen. U-42,126 was produced by the fermentation of Streptomyces sviceus. Its antimicrobial activity in vitro was limited to fungi. Certain bacteria were inhibited only when cultivated in completely synthetic media. U-42,126 was active in vivo against L1210 leukemia in mice.