Involved in the biosynthesis of the arabinogalactan (AG) region of the mycolylarabinogalactan-peptidoglycan (mAGP) complex, an essential component of the mycobacterial cell wall. Catalyzes the addition of an arabinofuranosyl (Araf) residue from the sugar donor beta-D-arabinofuranosyl-1-monophosphoryldecaprenol (DPA) on the C-3 of an alpha-(1->5)-linked Araf from the arabinan backbone of AG. Adds an alpha-D-arabinofuranosyl group from trans,octacis-decaprenylphospho-beta-D-arabinofuranose at the 3-O-position of an alpha-(1->5)-arabinofuranan chain attached to a beta-(1->5)-galactofuranan chain. Cell wall biogenesis; cell wall polysaccharide biosynthesis. Cells lacking this gene result in colonies with a more erose appearance compared with the usual glossy appearance. The mutant yields arabinogalactan (AG) with a significant reduction in arabinofuranosyl (Araf) content concomitant with a relative increase in the amount of galactanfuranosyl (Galf). It shows only a slightly reduced growth rate. Belongs to the glycosyltransferase 87 family.