STREPTOMYCES-ANTIBIOTICUS CONTAINS AT LEAST 3 OLEANDOMYCIN-RESISTANCEDETERMINANTS, ONE OF WHICH SHOWS SIMILARITY WITH PROTEINS OF THE ABC-TRANSPORTER SUPERFAMILY

Three different DNA fragments of an oleandomycin producer, Streptomyce s antibioticus, conferring oleandomycin resistance were cloned in plas mid pIJ702 and expressed in Streptomyces lividans and in Streptomyces albus. These oleandomycin resistance determinants were designated as o leA (pOR400), oleB (pOR501) and oleC (pOR800). oleA and oleC are close ly linked in the chromosome as they were both obtained together in two cosmid clones that were isolated from a genomic library. Sequencing o f the oleC resistance determinant revealed four complete open reading frames (ORFs) and the C-terminal end of a fifth. The functions of orf1 and orf2 are unknown since they did not show significant similarity w ith other sequences in the data bases. The orf3 gene product has simil arity with some proteins involved in iron and vitamin B12 uptake In ba cteria. The orf4 gene product had a hydrophilic profile and showed imp ortant similarity with proteins containing typical ATP-binding domains characteristic of the ABC-transporter superfamily and involved in mem brane transport and, particularly, with several genes conferring resis tance to various macrolide antibiotics and anticancer drugs. The last gene, orf5, is translationally coupled to orf4 and codes for a hydroph obic polypeptide containing several transmembrane domains characterist ic of integral membrane proteins. Subcloning and deletion experiments limited the resistance determinant to a 0.9 kb PstI-SphI fragment and only orf4 is included in this fragment. These results suggest that res istance to oleandomycin conferred by oleC (orf4) is probably due to an efflux transport system of the ABC-transporter superfamily.