Desosaminyl transferase EryCIII (, EryCIII) is an enzyme with systematic name dTDP-3-dimethylamino-4,6-dideoxy-alpha-D-glucopyranose:3-alpha-mycarosylerythronolide B 3-dimethylamino-4,6-dideoxy-alpha-D-glucosyltransferase. This enzyme catalyses the following chemical reaction
The enzyme is involved in erythromycin biosynthesis.