Abstract
Virginiamycin M1 (VM1), produced by Streptomyces virginiae, is a polyunsaturated macrolactone antibiotic belonging to the streptogramin family. The 10-kb regulatory gene cluster of VM1 production contains the varM gene, which encodes the type II ATP-binding cassette (ABC) transporter. This transporter is presumably involved in self-resistance to avoid suicide of the producer strain. Northern blot analyses revealed that varM expression is transcriptionally controlled by the VM1 molecule, but not by virginiamycin S, which is simultaneously produced to form a synergistic pair of the streptogramin family. Sequential addition of VM1 at increasing concentrations secured constitutive activation of varM expression, which suggested that the varM expression reflected an intracellular concentration of VM1. Heterologous expression of varM in Streptomyces lividans generated strains with no significant VM1 resistance. The mechanism underlying varM function in VM1 production is discussed.
