ABC-type transporter; part of the gene cluster that mediates the biosynthesis of the glycolipid biosurfactant ustilagic acid (UA) (PubMed:17850255). UA is a secreted cellobiose glycolipid that is toxic for many microorganisms and confers biocontrol activity to U.maydis (PubMed:17850255). Export of UA is presumably catalyzed by the ABC transporter atr1 (Probable). Atr1 appears to be quite unspecific, as many of the UA derivatives produced by cluster mutant strains are readily exported (Probable). Expression is strongly induced under conditions of nitrogen starvation (PubMed:17850255). Expression is positively regulated by the cluster-specific transcription factor rua1 that recognizes and binds to the specific 5'-T/G-G/T-C-G-C-A-T-A/T-C/T-C/T-G/A-3' upstream activating sequence found in all promoters of the UA biosynthesis genes (PubMed:20173069). Belongs to the ABC transporter superfamily. ABCB family. Multidrug resistance exporter (TC 3.A.1.201) subfamily.