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 decaprenyl-phospho-arabinose (DPA) on the C-3 of an alpha-(1->5)-linked Araf from the arabinan backbone of AG. It can also use (Z,Z)-farnesylphosphoryl D-arabinose (Z-FPA), and to a lesser extent (E,E,Z,Z,Z,Z)-heptaprenylphosphoryl D-arabinose (Z-HPA) and (Z)-nerylphosphoryl D-arabinose (Z-NPA) as sugar donors. 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 an increased permeability and an altered cell wall. Belongs to the glycosyltransferase 87 family.