TOPOLOGICAL STUDIES OF THE MEMBRANE COMPONENT OF THE OLEC ABC TRANSPORTER INVOLVED IN OLEANDOMYCIN RESISTANCE IN STREPTOMYCES-ANTIBIOTICUS

The OleC ABC transporter of Streptomyces antibioticus is constituted b y an ATP-binding protein (OleC) and a hydrophobic protein (OleC5). Her e we present experimental evidence demonstrating that the OleC5 protei n is an integral membrane protein and we propose a topological model f or its integration into the membrane. This model is based on the gener ation of hybrid proteins between different regions of OleC5 and a Esch erichia coli beta-lactamase (BlaM) and the determination of the minima l inhibitory concentrations to ampicillin in these constructions. Fusi ons were generated both by cloning specific fragments of oleC5 and by creating ExoIII nested deletions of the gene. In the topological model proposed there will be six alpha-helix transmembrane regions, two cyt oplasmic and four periplasmic loops and a hydrophobic linker domain.