Probable UDP-L-arabinose mutase involved in the biosynthesis of cell wall non-cellulosic polysaccharides. UDP-beta-L-arabinofuranose = UDP-beta-L-arabinopyranose Heteromers with RGP1 and RGP2. Localized predominantly in the cytosol. Widely expressed at low levels. The conserved DXD motif is involved in enzyme activity. Reversibly glycosylated in vitro by UDP-glucose, UDP-xylose and UDP-galactose, but not UDP-mannose. Belongs to the RGP family.