Promothiocins A and B novel thiopeptides with a tipA promoter inducing activity produced by Streptomyces sp. SF2741.

tipA gene which encodes one of these proteins was cloned and sequenced2). The tipA promoter (ptipA) was inserted in a promoter probe vector (pIJ486) so that it controlled the expression of a kanamycin resistance gene (pAK114). Although S. lividans (pAKl 14) was sensitive to kanamycin in the absence of thiostrepton, it became highly resistant to the antibiotic in the presence of very small amounts of thiostrepton (< 10~9m). Antibiotics structurally related to thiostrepton such as nosiheptide also induced ptipA, however, unrelated antibiotics did not. Here we report the use of this specific and sensitive assay to screen for thiostrepton-like compounds. Paper disks saturated with screening broth were placed on a kanamycin containing (5 jug/ml) nutrient agar plate seeded with a spore suspension of S. lividans (pAK1 14). After incubation for 24 hours at 30°C, a zone of S. lividans (pAKl 14) growth around the disk was presumed to indicate the presence of a thiopeptide antibiotic. As a result of this screening, APR. 1994